Straight Up

regardless of the other skills in a build, which one of these two skills is better/more useful to a party. If it makes any difference I'd rather it help PvP than PvE, but ideally it would be good for both.

Backfire: http://www.guildwarsguru.com/content/backfire-id399.php
or
Chaos Storm: http://www.guildwarsguru.com/content...torm-id401.php