Well - not too much experience - DSs are 4 and 1, so we're still into these things ourselves...
we have the Baby float seat (youngest may even have grown out of it, so let me know if you're interested - it was only heading for eBay anyway)
Certainly at age 10 months he really loved it last year, and it meant we could happily let him float around the pool with us, without having to hold onto him or anything...
Otherwise we used arm bands last year for the (then) 3 year old and that was OK, but a bit restrictive in his arm movements, and now that he is learning to swim we want to make sure he can move properly.
friends of ours have raved about the swimsuits with removeable floats in. Personally I have 2 concerns:
a) look more suitable for girls (girly swimsuit style?)
b) think both of ours would refuse to wear them.
Think we'll probably go for UV sunsuits with 'Konfidence' jackets - although I've also heard that if you don't get these quite the right size they can 'ride up' around their ears!
when and where are you off to in France? we're nr Ste maxime from 12 June.