The PBB will give you 1 support slot more than a BB2.
The PCA will give you something around level 50 with a good number of support slots and
that will allow you to do more in a GB than the average BB1. This is probably what you're
looking for.

Refer to the SailorExp vs. ShipLevel graph on Trainworld. ("Experience Gain vs. Ship"
under Sailor)

Once your sailors hit L61 and cap out of Blitz, the PCA will be a ways behind them and
closer to your supports.

Id go for the PBB because the Seva is a fairly decent BB
where as the pensa is an average PCA and not that usefull at lvl except as an AA ship.