If your new machine is powerful then I say install all the latest versions of popular browsers (firefox, Chrome, Opera, safari, ie).
Think of them as different cars, SUVs, van,...in your garage. Different browser for different purpose. One for accounts: email, banking, etc.. so this should be stable, latest version and have proper security settings. One for general browsing: should handle many tabs painlessly, install many extensions, good ad-block, etc. ...
Browser list:
Firefox 3.6.10
Firefox 4 beta
Minefield
Opera
Google Chrome
Google Canary
Chromium
SR ware Iron
Safari 5.x
IE