I think the Splashabouts Swim (got mine from darlingsdownunder) is THE BEST especially for containment. BUT, it doesn't undo, so if there is a poo in there, you have to pull the dirty nappy down bubba's legs. It wasn't an issue for me as DD started going to the pool at 4 months but never pooped while in the water.
For DS I recently bought a motherease swim nappy as it has snaps. Haven't tried it yet, though. I wonder how good any swim nappy would be at containing sloppy breastfed poos?

Sasa