For my mac, it (could) be Safari. JavaScript just seems to run flawlessly and it's very good with script (CSS3, webkit, etc) and it's very clean.
As for my PC, it's Firefox 3 Beta 5 for me
Very nice, tons of add-ons, clean. If Safari for PC wasn't as buggy, then I'd use that.
And last is IE, as it is in fact very crappy to use, but it allows me to download updates and etc (I use XP, not vista: I'll give it a few more months). Unfortunately everyone uses it, so you have to constantly use it for debug.
There is also Opera, which is pretty good. It has a "different" feel to it from all the other browsers. But, people still use it and therefore you need to deal with it.
And in fact, no browser is bad at all (we can hate them though, can't we? :P). Being a web designer, you need to keep in mind that you're building the website for everyone, therefore you will hopefully try to make the website operate/look exactly the same in all the browsers alike.
Personally - this is my list:
1. Safari OS X
2. Firefox 3 Beta 5
3. Firefox 2
4. Opera
5. IE 7/8