Frigates are super overpowered right now. If you're interested in minmaxing, I don't see how anything else is comparable.
Low supply costs, both for the hull and the crew, and high maximum speed mean they are the most efficient and best pursuit ships. They're also, generally, the cheapest thing to buy and outfit. Many variants can hold their own against destroyers and some frigates can destroy cruisers.
Right now, I'm rolling around with a lvl 36 character(C:7 L:4 T:10). My combat fleet consists of a flagship hyperion, a couple tempests and omens, and seven lashers fit with LDA, LAG, and annihilators/torpedoes. Hyperion is so easy to fit and fly for success. Tempests and omens are pretty good support. A lasher wolfpack can overload a cruiser, then use AAF on their LAGs for loads of armor/hull damage. This fleet handily takes out plunder fleets. I haven't taken an all frigate fleet against a tri-tach or hegemony capital fleet, yet, but I expect I could. The hyperion can kill an onslaught in seconds.
The only things I want to try are adding a few armor tank brawlers and a few annihilator rocket pod equipped vigilances. Armor tanking doesn't work too well and I can't find any brawlers. ARP-fit vigilances will be easy to get, though. Pods give the highest DPS of any missile. Just 4 vigilances gives you as many ARP's as an onslaught; that's 800 dps for 50 seconds. You've got a ton of damage even after they miss half of their shots.
Obviously, frigate fleets scale to lower levels pretty easily. You'll have tighter fits and tougher gameplay, of course, but you can exploit the 4 torpedo hyperion with just 5 aptitude in combat. The high tech aptitude is what buffs your wolf-pack's survivability and lets you fit it extravagantly, though.
The combat right now really makes me hope that starsector is successful enough to let (or induce) Alex redesign the engine to allow for multiplayer. Just based on what is in-game right now, a skirmish mode would allow for pretty complex decisions and meta development. Even the seemingly OP hyperion could be pretty easily countered by a human team, by using formations. Fitting a fleet becomes subject to cheese, like 8 gemini + a buttload of fighters and bombers. An opponent can fit more armor/hull tanking if he knows that you like to focus on kinetic/energy weapons. People might counter tachyon lances by having allies occlude them while they vent flux. TLDR, there's a lot of potential in the current content for emergent strategy and gameplay if you had humans as opponents.