Ok, well as we all know, energy weapons don't do much to hull so for max damage you're most likely looking at an antiproton build (crit boost) the other thing you want is resistances (high DPS=high threat level=very quick death) if you want an escort and don't want to spend real money i recommend the patrol escort, if you are willing to spend real money get the tactical escort retrofit or the multi-vectrol escort, the former is best for pvp the latter for STFs . use any and all energy weapon doffs relating to cannons. Other than that the only advise I can give you is that to achieve max damage use the tactical for this
For STF's most of the community will tell you to go Escort or go home and for good reason.
The best Damage will be the Tac officer in an escort. The engineer will give you some very helpful heals for surviving all the agg you generate. For an STF focused all cannon Boff layout I'd lean on AP:Beta 1 or 3, Scatter Volley 3 or 2, Rapid Fire 1 or 2, AP: Omega 1, 2xTT1, Polarize Hull 1, EPtS(as high as possible), and Hazard Emitters. Other powers would be negotiable.
Just like the others have said tac officers best dps / eng better survival
I play a tac officer and I have both the Tactical Escort retrofit and the Armitage (love them both)
If you are wanting to make a cannon boat stick with an escort. They are fast and maneuverable, and you will need this so that you can keep those cannons on target since you can only have them in the front. and they have the smallest arc 45 deg
That being said the optimum build is 3 DHC 1 torp front / 3 Turrets rear (these fire 360 deg)
I personally prefer Antiproton DHC myself but thats because that extra crit dmg is very nice. As for the torps quantum hit the hardest but photons fire more often (6.5 sec vs 8.5) so that's up to you, I rock quantum because the big crits with torps are very nice.
If you need any further help with gearing up an escort there is a really good guide on the forum here:
I use a Tactical Escort Retrofit with all DHCs and Turrets. I would recommend any escort for your all cannon build.
A lot of people like to go with Antiproton, which I would recommend you do. The best Antiproton DHC that can be bought from the Exchange is the Antiproton Dual Heavy Cannons MK XI [critd]x2 [dmg]. With it being a DHC and Antiproton, the critical severity is 70%.
I use Phaser Dual Heavy Cannons MK XI [critd]x3. They are pretty cheap, compared to the Antiproton. They do less damage per volley (because it doesn't have the [dmg] modifier), but the critical severity is the same (70%). I'm willing to take 5 less damage per cannon for the same critical severity plus the phaser proc.
Also, if you have a lot of EC, you can get Phaser Dual Heavy Cannons MK XII [critd]x3. Since I haven't seen any Antiproton DHC MK XII [critd]x2 [dmg], or any MK XII Antiproton DHCs for that matter, it would appear the Phaser DHCs MK XII would have the advantage in damage and proc.
As for DOFFs, I use 3x Shield Distribution Officers and 2x Hazard System Officers. Extra resistance and chance to do a shield heal.
Easy as pie dude. No other ship can deal the sheer damage of escorts. There are some cruisers, and even a klingon battlecruiser which can deal more sheer damage, but their turn rates do not support this. My suggestion, if anything is the defiant refit.
The refit defiant is simple. Uncloak with all your buffs activated, and fire away. If you get the fleet version, you can still fit the cloak but you get a bit more defense, the same bridge officer layout, and one more tactical console. To truely deal astonishing amounts of damage, fleet weapons are the best anymore. I can't speak on terms with elite weapons, but the advanced fleet weapons have four midfiers and are Mk XII items. They will deal serious damage. I'd also suggest a two part maco + two part borg set, so you can drain shields faster.
Aside from that, the sky is the limit. You can spend hundreds of millions of EC's on a single Mk XII very rare console on the exchange, so keep working on it.
If you want to go free, you can still get the fleet ships, but they won't have any special abilities, unless you get the fleet heavy assault carrier, which has a hanger bay. If you do plan on going free, you'll get good performance out of the fleet defiant, the fleet advanced escort, or the fleet blockade escort. The fleet armitage looks a bit decent, but it doesn't gain anything EXTREMELY special over the c-store version, just a bit more defense.
The only thing I can say is this: BE CAREFUL WHAT YOU BUY. These ships are grind worthy. taking time to get, so if you do plan on getting one, think about it, because after you get one, and you decide you don't like it, you're screwed, theres no going back.
I'm a tactical officer running the Tactical Escort Retrofit, and it can be a death machine set up right. I use 3 Borg Mk XII Antiproton DHCs and a Borg Mk XII Antiproton DBB up front, with Borg Mk XII Antiproton turrets in the rear. The DBB is there for beam overload, which when decloaking with buffs, is absolutely devastating. if you want all cannons for an escort, replace the DBB with another DHC.
I am the STO Lorax. I picked myself up and left, until the day the fun is replanted.