i use my 6.5 x 24 ruler and my 12.5 square ruler the most. i also have a shape cut that i like too but don't use as often. i have tried several mats and seem to keep coming back to my olfa mat that is the 24 x 36 size (or close to there) the most. don't forget to stop by harbor freight for those extra cutting blades!
where in az are you going to be? i have traveled around az a lot to local quilt stores and live in the mesa area so i could give you the scoop on some of the better stores if you'd like. :) enjoy your trip!