The best in my opinion is the Crewsaver Sea Baby, lots of buoyancy, a harness loop on the centre of the back, and the collar design seems more comfortable for them to wear than other types. It also looks like it will last them longer.
The Baltic is best for v small babies, but the lack of flex in the collar makes it less comfortable to wear as they start to walk and crawl around
Just Bought a Plastimo Baby Life Jacket. This has 2 Grab loops at the back and has stacks of buoyancy in it. Bright orange and comes with it's own baby whistle. These cost £25 with no vat on top as it is for children.
crewsaver seababy, brilliant and well made also lots of suffort for their head when they fall asleep. One of ours is now in the seachild same but a bit bigger.