K since I never shown my fits on eng forum, here… have some.
Grey falcon , atm fitted with Phase suppressor (way too good against destros), I was using the Sk’rah before that (same exact fit except for shaped charged shells) and before that the shrapnel (also same fit, for shrap with iridium slugs, if you know you will face good 'ceptor pilots: switch r6 implant to the third one (alpha inhibitor), otherwise for regular joes you won’t need that extra speed on your projectiles).
Yes I don’t have a proton wall, Yes If I’m captain this is not a good choice. Stay always safe, when you already used one of the heals, when you are outnumbered -> evade -> escape, save the offensive modules for later. If you get slow down, don’t feel ashamed to use one of the healings just to escape the slows (shield ones have a faster reload time, so you can use it most of the time for this without much remorse) and go under “cover” in order to counter attack later. Tacklers are meant to be your worst opponent after all, and a good pilot can blast you pretty fast if you don’t react properly by escaping his slowing modules and the target painter. Fed interceptors don’t have shield volume nor a decent hull to rely on, main “raw” defense are the resistances (and maneuverability oc), so if you loose them (slows=adaptive off): find cover asap.
Grey one is the best covy out there if you ask me, quite good bonus on rotation/damage/resistance make it even better than the Peregrine (I always hated the wobbly behave from peregrine btw). Don’t underestimate the combination between strafe and rotation, full rotation speed is nice for some escaping maneuvers, but for attacking ones, stafe in combination with rotation is kinda crucial. R9-3 is the key, If you get out of shields and healings for them, ffs avoid crashes  Btw notice that when your shields are depleted, your main defense is off, wiggle back home. But don’t forget tho avoid crashes in this case, since no shield=no protection against “white damage”. So don’t only rely on rotation, always combine a good strafe speed with high rotation.
Pro tip: while facing a target, try to turn in a direction with the mouse while strafing in the OPPOSITE direction, you will end in a quite cool maneuver, really good for dogfight and general purpose attack 8). Ffs don’t fly this thing on ping above 80 or with fps lower than 100 
Mjolnir
If you fly this thing the right way, you can’t die… unless your team failed completely or you overextended or if you loose totally combat awareness and get focused hard by being in the wrong position.
Once again: no proton wall. It have combat reboot and the Mj special module that remove any effects… that’s more than enough. It Is a ship for mid range operation, that means that in the range from 4000 to 0m you can shoot anything “bigger than a proper wiggling interceptor” and always hit. To be able to effectively shoot a good 'ceptor pilot you need closer range, I Would say, for them, starting from 2500m is ok. Not that I really notice the distance anyway, basically if I can’t hit someone 'cause he is too far and he is evading, IF I have still the speed module and/or the healing ready: I approach the target, deliver how many shots I can until I get focused, then: activate the speed modules (in case I need it, I spare my special module to retreat, not to attack, it is also really effective against ECMs while you escape since it removes “effects” and boost maneuverability not only speed) and healings, combat reboot if you need it → go back home safe. DON’T USE THE CHARGED SHOT UNLESS YOU ARE 100% SURE YOU WILL HIT. Shooting charged shots all the time is a waste on this gunship, when you have already a good alpha damage a_nd_ a nice rof and a good crit chance (all of them, and in case you need it, those can be improved even more by overdrive and or overcharge). Basically with this ship, you should stay with your team and next a good cover where to hide in order to heal and avoid fire. Only charge your enemies if you have one of the 2 combinations of modules to escape (speed+combat reboot or healing; Overdrive +heal or cr). Once again, always try to use the fast shot not the charged one, if you need more dps: use the overcharge module and the overdrive if you will not need it any soon. If the enemy “breaks” in your lines, just retreat, if you get out of modules and way to escape: try to bring to the grave with you as many bast… as you can .
Warning: pretty useless against destroyers and heavy survivability guards/command. Avoid to shoot at them if they are not already half hull down or in a really bad spot . Also, above 150 ping this fit is less powerful.
Mauler
That’s a fit mostly made for survival game mode (fast reload for the modules and the rank9-3 implant to avoid die miserably by crashing). Probably Kraken will offer an overall better suite for the positron cannon
but the fact is that I already have the Brokk, so by using the mauler and winning game, I’m farming monocristals with it. Also the Mauler have quite some nice bonus due the rank (+10 and +5 to the damage, and iirc +30 to resistance). Charged shots here are quite the way I use the Positron (at least against fighters and 'ceptors), the key with this gun is to achieve the best projectile speed in order to be able to hit pretty much anything at the right distance (around 3000m for fast target) timing the normal shots with the charged ones. NO minelayer, it is useful indeed, but it have the drawback of making you pretty visible on the map. Something that you want to avoid all the time since in order to acquire good firing range, sneaking in cloaked is the way to go here. If you get detected by an enemy approaching, activate reverse trust, the resistance buff module and shoot a blue torp If you have the “angle”, right before the jump shoot a guided torp to the nearest enemy. Sound tricky but after a while you do this it will become quite easy. Remember that your main gun is the Positron, the guided torpedo is only situational when you are doing this, even more: shooting a guided torp will most probably get you detected. I’ve used this ship with good results on high ping server (150 and up), ping compensation mechanic works quite good for shooting, way less for moving around, but most of the time you will only slide around and don’t use your trusters anyway
Pro tip: when you are in an engi, PLEASE don’t shoot with your healing weapons toward a friendly LRF hiding in scattering field between enemy lines. Healing are nice, but if you let the enemy to detect me, you are not doing a favor to your fella.
Another worthy advice is: don’t sit in respawn (obvious) or sneak in obvious position like the center of the maps or the top of them. It’s supposed to be “space”, there are other “directions” where to hide and shoot to enemies avoiding being detected. Usually players tend to not look so often to the bottom of the map for example.
Brokk
First off: this is not some sorts of “guide” for normal engies, this is not the tankiest engi out there and it cannot be used as an Octopus or a Minotaur/Naga. But the healing output tnx to the main gun is pretty damn high. Try to avoid being focused at all, stay behind cover next to your best team mates and heal as much as you can. Shooting at opponents, it’s quite an “optional” (not shooting too much at enemies will also prevents you from being targeted).
As I’ve said, this ship is nowhere near tanky and “forgiving” like other engies, main good thing it have is the healing weapon. Spoils it by staying in range with your allyes and by don’t use much the aftherburners since the gun consume tons of energy (also the r12-2 implant gives a nice boost on energy combined with a voltage regulator if you don’t move too much around). Use the blue torp only for self defense when an enemy focus you and get in close range. Otherwise try to spare them. Not that much to say after this apart: don’t focus your healing gun only on allies destros, other ships can be healed really fast by your gun, if they are in range; heal them first, than the destro (you have also other modules for healings, dessies will survive with those… hopefully). Last tips: maybe in an organized squad vs squad scenario there are better engies for the job. Last one: don’t get focused, uhm I’ve already said that? Well let me say it again: don’t get focused  and don’t move around alone, if your team is late on beacons, don’t go there alone (engies 101 :P) or if you are outnumbered hard.
More to come: maybe Cyning + Saw one