I've played on both sites using their PC clients, and while they're both fairly slick (especially compared to Party Poker's awful software), I prefer the interface and look of Full Tilt to that of Poker Room. Your tastes may differ, so try 'em both out.

The games at either are fairly comparable, esp. if you're just looking for low stakes limit or no-limit hold'em.

The nice thing is that both sites offer huge signup bonuses for new accounts.