Despite having cross-browser incompatibility issues and various things breaking and being re-done with each release, I’m firmly in the jQuery camp and am actively building new things on top of it. This likely includes a port of PHP Tag Engine to jQuery, as well as many of my WordPress plugins.
It’s like the old story:
Youâ€™re a coach deciding between two runners. They both run the 100m equally fast. One has perfect form. The other has terrible form. Who do you chose?
You chose the runner with terrible form. Why? Because when he finally has perfect form heâ€™ll wax the floor with the other runner.
YUI and Prototype/Scriptaculous are much more polished now, but I see the ease of authoring in jQuery to be too big a developer benefit for it not to rise to the top in the long run.