I could see how a twin blade might save fractions of a second and possibly save a canoe from a big rock in mad rapids, but I'm not doing that. Other than that I have no need to change sides that often; my J-stroke is just fine.
I prefer fairly huge-area paddles with a long handle, and I bought one such instrument on sale, the canoe came with two fairly standard wooden paddles with fibreglass tips for wear. I would like to try out a bent-shaft some day, but it's down on my list; I'm spending all my money on GPS, skis, lifttickets etc.
I'm not averse to advice on which wood or other construction would give me a lighter paddle though, just in case my daughter ever gets some stamina and I have to spend a long day on the water (She has some stamina; she can swim for miles and miles, but she seems to get tired of paddling after only a half dozen hours or so, and she can't ski all day either
: . Maybe it's a question of effeciency.).