What my kids dont like are the regular round tubes that you can sort of sit in. The round tubes that have the cover that go over the center where the rider lays on top seem to be best when talking about a round one.
We have a Rave Razor that the kids really like. The nice thing about it is that it is perfect for two kids (or adults) to ride in and if you have just one person, they can sit on the top and ride solo.
This is my friends tube, which is the round and flat version they seem to like:

Here is the Razor:



Also...as you can see...the Razor has a little rooster tail, which is cool. Its available at Bass Pro...and on sale now I believe...just threw away my Bass Pro ad, but recall seeing it in theere.