Catching up!

So I leveled my Priest solo to level 77, since I didn't want to pay for another set of WoTLK for more than one account. (Money is tight across the board these days).

But, I got my tax return and would love to get my rogue caught up.

Would it be a better idea to solo quest/level my rogue. Or would it be better to bring my priest back and get him caught up?

I was thinking ding 80 on my priest and then go back to get my rogue caught up at a later time. (Of course the Party EXP will be less, but quests will be done quite a bit faster)