1. RM Giulio Cesare (1914). Multiple good armament options, excellent speed. Extreme firepower. All around great ship to play. The only downside is its size, which makes it a fairly easy target, at least compared to the Ciao Duilio.
2. USN New York. Absolute blast to play and a devastating opponent in capable hands, even for BB6s and Baram (monster ship). However, that thing is slow, which is why the above ship wins out.
3. MN Le Havre. Reasonable speed and excellent firepower with quads. Poor spread knocks it down a bit though. A decent ship with alternative armament options too. Gun setup is a bit awkward (1 fore, 3 aft), but good traverse helps counter the problem.
4. IJN Shinano. One of the few EBBs (above EBB1 tier) with its own guns, the Shinano is a blast to play and an opponent to be feared. It gets put well ahead of many contemporaries due to its options and blockshotting goodness.
5. IJN Hyuga. Despite the awkward gun setup (2 fore, 4 aft), 12 16" shells that pretty much can't be bounced make a nightmare opponent for all AWs and a major threat for anyone else. And, just for good measure, you can load with with Mikasa guns and zip around at 45+ knots with CA reload - a blast to go into W@W with. This option allows it to inch out other high-powered ships in its tier like the Maryland and Bismarck '43.
Honorable mentions:
-IJN Mikasa: A fun ship to play, but the reload doesn't even come close to compensating for the tiny number of guns and poor shell damage. It has quite possibly the lowest firepower of any BB, but is indeed fun to play. And you get a special feeling whenever you somehow manage to sink a BB4+ with it.
-KM O-Project II (1942): While hardly different from its regular counterpart (slight speed boost, extra support slot), this ship is insane in the right hands due to its speed and tight spread - while maintaining solid range - and is notably different from most other KM ships in play style. It also has additional options, though I don't really consider the 16" Ns viable.
-RN Temeraire: It's the paint job. The ship is nothing spectacular, even having less supports than lower RN ships, but it plays decently looks great while doing so.