#6 doesn't have enough color in the logo/symbol itself, considering the fact that the background will vary depending on its use. On t-shirts, it may be a white shirt... but on a web site, the gradient or background may vary over time.
I'd like to see a more "bubbly" Web 2.0 font treatment, but I like where you're going with the lettering in #5 and #6. In #5, see if you can use brighter colors instead of black to white gradient. Thanks!