I have 2 KDF Lt. Generals, 1 Brig. General and 4 Captains.
I have 1 Fed Vice Admiral and 2 Lt. Cmdr's.
As you can see I enjoy spending my time on the KDF side much, much more. Part of it is the community and part of it is the inane Fed content. I mean how many times do you get tricked by the Udine into doing something stupid as a Feddie?
My Klingon (Valias) was my first main, even though I planned from the beginning to have a character in every faction. However, back then, the KDF had extremely little content and 100% PvP wasn't really viable for me on the long run, so at roughly T3 (the "lean period") I switched to my Vulcan Scientist (T'Lana) who happened to become my first max level character, overtaking Val. She used to fly a Nova until T4, briefly switching into a Cheyenne-class, but now commanding an Excelsior.
I grew weary of all the Fed whining about carriers (or KvF PvP in general), so I decided my next character would be a Fed Tactical escort captain, showing people how it's done, so I created Kaylen. She's yet got to reach T5 and actually get into a match with a carrier, but so far she has done nicely in PvP matches, faring fairly okay in space (definitively more wins than losses and being a good teamplayer) and absolutely pwning people on ground with her hand-to-hand maneuvers.
Then it was announced that we get a T5 version of the B'rel, which is one of my favorite Trek ships ever, so I knew instantly I had to get Val up to the General tier because, by Kahless, she needs this one! Fortunately the devs also rolled out some new PvE content, so I took this as a chance to experience these new missions as well. Together with a rekindled interest in PvP, Val blasted through the last couple levels and reached the rank of LtG a few weeks before the B'rel hit the C-Store. Since she still had a ship token I didn't even had to buy it for CP. Qapla'!
The reason that Kaylen isn't yet T5 is my newest character, the Orion Cora, who started out as one of Valias' Bridge Officers and was recreated as a player character for both roleplaying as well as experiencing another angle of the KDF (stylewise). Naturally, the end goal here is the Marauder Patrol Cruiser.
Right now I'm balancing my attention between Kaylen (whose Akira has a fittingly devastating torpedo salvo - did you know that High Yield buffs do in fact stack?) and Cora (who sticks to the Raptors for now). The latter can regularly be seen prowling Pi Canis on the lookout for easy plunder.
So, this is the evolution of my characters, not counting any "one-offs" I created and deleted again. As you can see, I've had a lot of fun in STO, and a good deal of it happened on the Klingon side.
I am the type of guy that ends up making 50 characters for primarilly aesthetic value... or to min/max a build I am trying out. When I first got STO, I created an alien fed tac officer. I ran through the game, learned a lot and then created a Klingon Tac officer to see if I could do it better the second time around.
I got to about Cmdr 5 and due to lack of content (It was like 1 1/2 months from launch) on the Klingon side, I created an Engie Cruiser fed... then got tired of my Tac captain so erased her and made a sci officer... got bored of my tac Klingon, so I erased her and made a Kling sci (Still have that one, "The Reagent") then made ANOTHER alien tac captain on the fed side (Still have that one) Then ANOTHER sci fed... sigh... so on and so on...
Yeah, I have 6 full character slots... 'finished' the game (Reached max level) with 4 different fed characters and 2 Klingons... and out of all those original characters that finished the game... I have only 1. I have replayed the fed side twice through with all three officer types.
Right now, due mainly to the new weekly episodes that have come out and in anticipation of more soon... I now have 4 Klingons:
The Reagent, LtGen Sci Alien Carrier
Jattari, Cap 6 Tac Orion BoP
Cytheria, LtCmdr 3 Tac Alien Raptor (Crafter)
Hiroe, LtCmdr 7 Eng Alien Cruiser
And only 2 feds:
Lunari, RA upper Tac Alien Escort
Noriko, RA lower Eng Alien Cruiser
So counting all the characters I have leveled at LEAST to RA/BG, and enevitably deleted... I have had about 13 characters total. Thats NOT counting 2 characters (Klingons) I ended up deleting at Cmdr level due to boredom (lack of content before season 2). Nowadays though, I actually LOVE leveling my Klingons, and its only getting better!
I like to experiment allot, problem is I make a lousy scientist as I get attached to my experiments and keep them. Right now I have a hoard of thirteen active toons. That does not count about eight restarts. I have room for one more toon but may buy another two slots to make three Rommies when they hit. As it stands right now I have three Klings and ten Feds, (I did most of my experiments on the Feds early on). Still I'd like to have one each career types for every faction in the game. That said "main" your fave, but don't limit yourself to your main.
After taking around a 7 month break played a Tact Fed and a Sci Kling - this is alongside my original Fed char of a Eng...and the only one who is at level cap is the Kling...
My Kling is probably my main now due to it being the better geared, and more fun to play...the Eng Fed runs a Sci ship and is very low dps and boring; the Tact Fed runs a Adv Escort and I can't see anything to work to (unlike the Kling who I wanted to try the T5 Carrier and Patrol Cruiser).
Kling is good but very repetitive with the low amount of any story lines (although what is given is better than Fed side imo)
At endgame, the things available to do are the same for both sides. Grind out the same dailies to earn emblems, or crafting materials. Leveling up on the KDF side there is more repetition. For the feds, you just have to fly around a bit more for your repetition, and there are a few more story based missions.
KDF offers some unique ship options that may or may not fit your play style.