As PBBs were just explained, I'll go into EBBs. The original EBBs (now EBB1) were intended as fun ships that often had very unusual attributes. Depending on the ship and your play style, you may or may not find it more rewarding than a PCA (both PCA and EBB1 are basically BB 0.5), but unless you're relying heavily on shared exp, it will give better rewards than a regular CA2. Compared to BB1s, EBB1s are better at high levels, and give that bonus for attacking higher level ships, but most will find the PBBs to be better than them.
EBB2s are basically BB1s or BB2s with more support slots and BB3 guns. As you might expect, the range advantage again makes them perform above level, but it's a combination on individual stats and preference (as in, depends on the nation and your play style) as to whether they're better than PBBs, which are similar level.
EBB3s are usually BB2s that are upgunned to BB3 level. The big deal here is that most of the chosen base BB2s have a high number of guns (or can at least be set up that way), usually resulting in firepower about 50% higher than the nation's EBB2. Most EBB3s also have more firepower than many BB4/5s, and Again, they have more support slots, allowing them to last long enough to use it. A well-played EBB3 is a huge threat to most ships, and therefore racks up a lot of exp.
However, by extension, some BB2s can be pretty impressive themselves. For example, my experience is that for IJN, the Fuso is the best ship for levelling crew until at least EBB3 levels (and BB4 if you don't have one). It has as many support slots as the Nagato, almost as many as the EBBs, has a smaller profile, holds more bulge (important!), has decent spread, and can consistently 2-3 shot BB5s if it gets in range, even withthe weaker guns. At that level, the experience bonus can be quite significant. It also has better gun setup than the EBB3.