Firefox. With the range of add-ons available, it's an easy to way to virtually make your own browser. My current add-ons:

Noscript: Javascript switched off by default, but you can enable it for individual sites. This cuts out one of the most common causes of nastiness, unless you actively let them in.
Adblock: Can block individual objects such as images, or entire ranges, such as anything from http://spamstuff.com/*.
Flashblock: Disables flash by default, unless you enable individual objects. No more memory leakage from flash unless you actively decide to let it.
Menu Editor: Easy way to manage overlong menus, both on the toolbar and context menus. Remove the items you don't want, and arrange the ones you do want so it's tidier.

Most IE and other browser functions are replicable with one add-on or another.