My Favs:

DD was the ddx, was fun and had decent damage
CL was the Brooklyn, crazy fun when you get a decent crew in blitz
CA was the Baltimore, tough, fairly fast and able to mount ample ammo binds
and guns, was a fun CA.
BB1 Alot of folks hate the suckvada but I enjoyed it over the Alaska.
BB2 Penny one of the funnest ships Ive played especially with the remodel
BB3 S. Dakota with one historical glitch...i dont like how it only has 4 t mounts
(for AA) when the N.Carolina has 5. Historically the Dakotas had 5 t mounts
per side to mount 10 5 inch barrels for AA purposes or as a secondary battery.
Any BB above this is a hoot to play.

I agree the US BB line is easy and fairly fun line to play at later levels.

For CV's I really REALLY liked the Essex class, one of the best. The PCV is
really nice too. I did enjoy the Yorktown especially once I had decent bombers
and fighters. Generally speaking US CVs outclass your opponents. Airplanes
are a different matter :p.

I would have to say BB and CV because both are very good after the patches that have
happened mainly the CV line but the BB line is great if you like to play an easy ship.

USN SS has some pros but some bigger cons
Pros
SS1 is one fast little devil that dives like a brick
USN SS gets extra salvo(faster reload then KM UK IJN etc)
USN torps are devistatingly effective against big and small ships

Cons
extreamely expensive(SS1 is 765k)
SS1 gets less torpedos
no proxies
accually requires the player to aim :D

Its largely dependent on your playstyle and preference. US is the jack of all trades with
no major advantages but it also has no major weaknesses.

US CV- good Carrier ships and ftr pilot stats,
US T4s are among the best
US DBs are not as hard hitting as IJN or MN (idk about soviets)

US BB- Has the Highest BB5 damage,
BB3 South Dakota is a speed demon with good engys
Low to medium range for BB guns
Spread is....horrible to say the least with At level Gunners

US SS- Cant comment (havent played this much)