I leveled pally + priest and it's awesome so far. Just dinged 55 last night (51 when I started playing, and I only played for 2 hrs).
Pally = ret
Priest = disc

You can pull like 6 mobs at once, use Consecration, bubble up, heal when necessary, etc. It may be confusing to set up the macros at first, but after level 20 or so, you kinda get the hang of it. And besides, level 20 is not that hard, it's only like 6 hrs of playing =)