One feature I look for is the the ability to auto-refresh a page. AvantBrowser has it and MyIE2 has it (Opera’s has it, too, but I’m concentrating on IE-based browsers for the time being). The auto-refresh UI’s a little slicker in AvantBrowser but, operationally, it seems to work just a tiny bit better in MyIE2 — in AvantBrowser the page sometimes will lose focus during an auto-update and at other times the AvantBrowser windows will pop to the front. I don’t seem to have that problem with MyIE2.
Another feature is form-filling. AvantBrowser relies on AI RoboForm for it’s form-filling capabilities whereas you can choose whether to use RoboForm or the form filler that’s integral to MyIE2. RoboForm comes in two flavors: a free one and a paid one and is supposed to be pretty powerful with a lot of bells and whistles even in the free version but, personally, I’ve never had a problem with MyIE2’s built-in support which is why I continue to use it.