A rim with a rolled lip is definitely the way to go for XC, trail riding, etc. (unless you want to spend the $$ on bead locks or reinforced wheels). Even the heavy duty .190's that aren't rolled will ding easy.  Also when buying rims the first number is the amount of back spacing, so a 3.0 + 5.0 will have an offset of 3" on the inside and 5" on the outside.