There's no "better." All of them had some really broken ships early on, but those got fixed (sometimes a little too aggressively).
In general, Soviet BBs have long range, high firepower, and are a bit weaker on speed. Their CVs have the best DB in the game, but weak fighters.
In general, Italian BBs have low angles and decent reload, but less firepower and range. Their CVs have the second best TB after UK.
In general, French BBs are either fast with decent firepower but low range, or slower with high firepower - and still low range. They're generally middle of the road in most areas for CV.
All lines have exceptions, but those were the general traits. At top tiers, French has the most aggressive BB6+, Soviets have some of the best line fighters after KM, and Italians . . . have arguably the worst top tier BBs, but some of the best lower and mid-tier ones.
