Well, let me barge in here for some tips, but i’m gonna start with a no-no: jr, it’s better if you don’t ask these kinds of questions if to choose A or B (not bad mouthing, pls don’t misunderstand; just trying to help, read on). It rather goes down to personal preference, experience and ‘feeling’ how something works for you in the end, not what others tell you to use of A or B. Long ago for example people have been telling me assault rails and plasma guns were the way to go. Then i discovered Stab Rails (old version of Gauss) which topped the rest in my play style by a fairly large degree. Just letting you know how to phrase it next time, so it’s better to ask for opinions, general pros and cons etc, this kind of stuff (the thread ultimately went down to this, no problem), but not ‘A or B?’.
Of course that for one current patch changes will make a certain weapon probably stand above others, so if you can aim properly with it you can safely use it till it gets nerfed or a weapon you used better earlier gets buffed over it compared to your own efficiency with them.
About grinding, i suggest you do it this way: grind each subfaction of each 3 factions to Rank 6 at first, then 9, then 12, then 15 (T1 doesn’t matter). If you cannot decide which one to start with, go to the warehouse, find the first mod(s) that you would like to use first in the future and see who unlocks them. This type of grinding is also recommended to save up credits for proper ship fittings once blue items are unlocked. It is also a good option to grind a part of the next 3 subfaction ranks up in the tier you are currently on, namely 2-3-4 of them before hopping into their tier - credits saved and at least a few better mk3 blue mods to choose from when entering the new tier. As an example: stay in T2 until you get 2-3-4 subfactions to Rank 9 before joining T3. There are plenty of people who rush a certain ship line to tiers 4-5 only to find themselves nearly unable to do anything at all compared to other players because the maximum they can have is MK2, possibly VERY FEW militaries and i really doubt about purples. Militaries may not even fit on their chosen ship line as well.
As others said the singularity cannon is atm among the best choices in PvE for gunships. For PvP basically you will have to try them all out 1 by 1, there IS NO BEST here, it is just which one you feel to be better for your play style (or if some weapon got super-buffed in the last patch ).
Singularity cannon is also one of the better choices on command ships if you ever decide to fly them. Don’t fall in the ‘Gauss trap’. Test them for yourself before deciding again. Not a single Gauss fitted command ship has killed me so far, they barely damaged me - true story.
I haven’t flown these in a while since i kinda hate all the new guns they received. Better base off what others have said so far.
However when i fly them i pick Coil Mortars usually because of the AOE detonation hit that increases hit chances with the proper fittings and also deals good amounts of damage. Heavy Blaster and Positron Cannon also deal massive damages. Heavy Blaster is the hardest to aim and it requires close range combat for maximum effectiveness as far as i know. I believe some people will state the other way.
I consider Beam Lasers a utility instead of a gun. Just like Gauss on command ships, these have never killed me yet, only damaged a bit. They have weak damage, great range, their main use IMO is suppresive fire, decloaking and stopping enemies from capturing beacons (hitting an enemy interrupts their capturing process).
Hope i helped, good luck!