i advise you go with a smaller one. the bigger ones require a ton of weed to be inside it at once in order for it to work properly. if your just trying to grind up a bowl youll be twisting that thing for hours. my friend had a 5 incher that was pretty worthless to say the least.
imo 2.5 is the perfect size. I have a 2.5 and a 1.25, and the 2.5 is perfect. Just be sure to get a good quality one.
i got this, think i was a good deal? http://cgi.ebay.com/2-5-MAGNETIC-PO...132326186QQihZ010QQcategoryZ133QQcmdZViewItem