I was going to buy one of these SP dynamo hubs
I settled on a Sanyo because the vendor didn't have the SP listed at the time.
The Sanyo impresses me as having as much drag as the cheap Shimanos, which seems like a lot when you are holding the hub in your hand, but isn't noticeable on the bike. The more expensive Shimanos are pretty draggy in your hand, but not as bad as the cheap ones. Again, I can't tell the difference on the bike, and I out-coast a lot of people I ride with so the drag can't be too bad. The Sanyo is on my cheap 650b conversion project, which doesn't have a frame yet so I haven't tested it.

I bought a cheap ($60) 26" Alex rim/Shimano dyno wheel. The hub is ok, but the wheel is a typically poorly machine-built wheel. I did think about getting the 700c version for my daughter's hybrid, haven't gotten around to that yet