Tactical Escort Retrofit is a good choice usually.
I used that one until i got the fleet version of it, which is even better
And if you dont want to spend a great deal of Zen until you know you can always test some of the new mirror escorts like this one http://www.stowiki.org/Mirror_Universe_Advanced_Escort
Not that expensive on the exchange.
And not much that differs from the retro defiant one.
I don't have a Multi-Vector Advanced Escort, and none of the friends I usually play with do. So I can't comment on that.
Regarding the Heavy Escort Carrier and Vesta Pack - a hangar slot is always a good thing, and there's really no drawback. In a way, the gameplay is probably similar, since both would be relatively fast-turning ships probably using a dual heavy cannon loadout, and with fighter/shuttle pets.
The Vesta is interesting. The fact you can slot three Aux Dual Heavy Cannons in the front is nice, having them run off Aux power instead of Weapon power makes energy management a lot easier in a Vesta. It plays a lot like a Science/Escort hybrid if you do this, and many people do. A real Escort will still do more damage, but it's a lot of teeth for a science ship. I'm not really convinced it's worth paying for the Vesta Pack, though.
Yeah, I got it, but I also have a lifetime STO subscription and had a hell of a lot of C-store stipend banked.
I don't actually have a Heavy Escort Carrier, but a friend uses the Armitage on one of his VAs, and we've compared it, talked about it some.
The MVAE has a big Science slant with it's Lt Commander Sci station. It's a potent ship with that slot. A lot of nice combos can be had. Gravity Well to compact a group of ships and the open up with Attack Pattern Alpha + Cannon: Scatter Volley and then a Torpedeo Spread for flavor. But you it's sacrifices the Lt Commander Station that other Tier 5 Escorts have.
I hope that you got an Advanced Escort for your Level 40 ship choice. You can take the MV console of the MVAE and put into the Advanced Escort. That would give you the looks, and MV ability along with the Lt Commander Tactical slot. That would allow you to get a Cannon Skill II or Torpedo Skill III which definitely would increase your damage output. And you would have the Lt Science and Eng Science stations for a lesser science slant.
The Tactical Escort Refit is just a DPS oriented ship. It's a bit less survivability compared to the other T5 Escorts. But it's a quick, agile and packs one hell of a punch. And you can run two Tactical Teams back to back w/o sacrificing an Ensign tactical slot.
My only problem with the Steamrunner is the ensign science slot - hazard emitters are pretty much a requirement. You don't really have access to half of the shield regen abilities if you want to be able to cleanse the more dangerous hazard on it.
Getting back on topic.. Honestly, the Patrol Escort(and its fleet variant) is an excellent ship that has all the firepower you'd expect from a tactical ship, but can also take a respectable amount of punishment. (The Mirror Patrol Escort is the same, statwise, if you prefer the look of the advanced/MVAE.)
If you're really wanting a C-store ship, it would probably be difficult to do much better than the Armitage. It's a solid ship with the teeth of an escort while also having some extra flexibility. As an added bonus, you can get a lot of ship part customization for it - There are five different variants of the Akira Chasis(Akira, Oslo, Zephyr, Thunderchild, Armitage).