Hexes vs. Squares
It depends on much you use miniatures in your game. WotC seems to be trying to steer everyone towards that end (maybe because they have a new line of miniatures coming out soon?), but I know lots of gamers, including myself, who didn't use mats or miniatures and got along with role-playing just fine. I like miniatures now, and I actually prefer a hex-sided mat, but I have a square-sided one, too. It all depends on what the DM and players for your game like and prefer. You don't even have to use the rules in the PHB - you could make up your own or revise them to fit your needs.
-Collin