Well, a bit more complete:
"ECL" Duca Degli Abruzzi: Haven't used, but intended gunset are 5.3"/45 Model 1938 (2 twin, 2 trip), but can also mount 6", 7.5" twin & single. Those, plus more supports than similar-level DDs and CLs make it great for leveling crews in GB. However, I just use the Capitani Romani (smaller size) and eat the low level exp penalties.
PCA Zara: The intended 8"/53 twins are decent guns, but are a wild departure from every other RM gun (45 degrees). It can also mount all other CA guns, though they're suboptimal. With that in mind, it's only real benefit over the regular CAs is the extra support slot. And to counter that to a degree, it's quite large and easy to hit.
PBB Andrea Doria: Intended gun set is the 12.6" trips and twins, with the "AD" 3.5" singles and 5.3" trips for the secondary/AA battery. Basically similar to the KM Andrea Doria with three major differences. First, it hits the hardest of all PBBs. Second, it carries more ammo, so it doesn't have the KM's problem of running out on the trips in long games. But, to counter those benefits, it's SLOW. In fact, it's in contention for the second slowest BB in the game (only SN BB6 is slower). With the relatively limited range accorded PBBs, this is a serious liability, and makes this much harder to use well (and therefore not as great for leveling). Especially with the excellent BB2s that RM has access to, this would be the one PBB I would most recommend skipping. Still a good ship in skilled hands, but you can get better from the tree.
EBB1 Re Umberto: Intended gun set is the 13.5" twins, which have been nerfed (angle from 20 to 30). Even with the reduced capability, the small size makes you easy to miss, and you do get a decent AA battery and BB3 supports. Not bad as a fun ship, and the low level makes it an alternative to the Zara.
EBB2 Dante Alighieri(1914): Haven't used, but it has the same supports as the regular Dante, but can mount the 12" Model 1909 trips instead of just twins. Or, if you want to have some fun. I also occasionally see it with the 12" twins for boosted speed.
EBB3 Giulio Cesare (1914): Arguably one of the best EBBs in the game, and probably the best in its tier. Intended guns are the 12" K10 twins and trips, but can also mount 5 12" 1909 trips, or the range of other twin BB1-2 guns. In all setups, it is very fast and has extreme firepower. Regardless of the setup, this ship is FAST (45+ knots), a blast to play, and can terrorize any other ship in the game if it gets into range, which is not that hard with its speed.
EBB3.5 Caracciolo (1919): Exact same gun space and number of slots as the basic version, the only difference being the BB5 supports. This is a solid ship but, like its normal counterpart, plays quite differently from most other RM BBs due to the low gun count. Aside from the low gun angles, it doesn't have any special advantages, but is at least adequate for leveling. It's also slightly larger than the regular Caracciolo.
EBB4 Giulio Cesare (1940): As with all EBB4, this is a basic BB4 with BB5 supports and not much else to note in differences. Good for leveling, but nothing special. However, it's hurt hard by the EBB4.5, which is almost the same ship and more.
EBB4.5 Leonardo da Vinci: This is a GS40 with 1 less knot in speed and 20% more firepower - mounting 4 trips instead of 2 twins and 2 trips. It's unique among its tier in that it uses regular BB4 guns and has no viable BB5 weapon options. In exchange, it has the same supports as the EBB4s, and is therefore almost a strict upgrade on the Giulio Cesare '40 at only 2 levels higher. This is generally regarded as second only to the Giulio Cesare '14 as an RM EBB choice.
EBB5 Cesare Borgia: This is a Vittorio Veneto with larger size and one more support slot, and not much else. Unlike most EBB5s, it has absolutely no alternative gun sets to the 115 VV clones (regular VV gun only fits 1 bind, and is therefore not useable). It has all of the strengths and weaknesses of the regular VV, which makes it an overall lackluster ship. Recommended only for completists, those who want to be able to level an entire BB6 crew at once, and those who might use it to "power level" CV and SS BOs.
EBB5.5 Gaius Duilius:
ECV2 Rota (1925): RM is one of two nations that does not have an ECV1. Instead, its first one is at the same level as other nations' ECV2, and is basically a CV3 with 1 more support slot and 1000 more plane space. It's a somewhat adequate way to help in the grind to CV4, but is completely outclassed by said CV4 7 levels later. After that, it's value is very limited.
ECV3 Sparviero (1943): This does to the Sparviero what the ECV2 does to the Rota. You get an extra support (now CV5 level) and 1000 more plane space, but same max takeoff. However, being at higher level, this ship has much greater utility even after you've gone on to bigger and better things - which itself takes a much longer 9 levels. The Sparviero '43 is also notable in having the highest sale price (not trade, sale back to the yard) of any event ship, and if you have medals or coupons to spare, can help you get those last credits and points for a BB/CV6.
PCV Progetto Gagnotto: As with all others, this is an amazing buy for the money, and gets you a ship that's literally a full tier above your typical CV5. Nothing special on this one compared to the others, but if you're running CVs and not getting this, you're doing it wrong.