I bought the Neoprene one from Dick's, on sale for 35.00. IMO, it's great. I've read the nylon ones get real hot. I also found that these ones don't seem to be so bulky, and fit around the head better.
When we test fitted it for him in the store, I put it on him, and picked him up by the handle on the head float, and hung him on the wall. He didn't seem uncomfortable at all.
I have found that when he's in the water, since he is only like 14 pounds that it's slightly big for him, and the unless you unzip the top just a tad the corners poke him in the face. When in the boat, we keep it zipped up. I don't care if it pokes his face if he goes flying out, atleast he'll float.
This is my son (10 weeks, and his partner in crime, who is 5 months.