i tend to like large mice that have a bit of weight on them. but then, i have big hands. ignore fancy DPI and response time.. you wont notice a difference playing RPG's. pay more attention to how many programmable buttons it has and the drivers/software they use.. some have 'programmable' buttons but theyre only programmable within a preselected drop down list.. as opposed to being able to assign your own keystrokes.

i use the logitech G5 as my main and 4 $4 generic IR mice for the clones. its big, it has lots of extra buttons and logitech software is nice.