Any cheap one with 2 buttons and a wheel is all you need. Next question... jk xD
If you are into games like mmorpgs and stuff having a couple macro buttons is usefull and practical but not extremelly needed. Also, personally I don't really like heavy mouses, I prefer a medium-light weight one. Size wize I have used both big and small mouses and there is no difference since your brain just adapts to the shape in a couple hours.
Personally If I went for a gaming mouse I would aim for a good price/quality ratio. Also a mouse pad might be good to get too to make the most out of the mouse