Personally, if you're planning on 5-boxing, I'd go with four new accounts plus the original.

RAF leveling leaves you extremely cash strapped; any amount of gold on an original toon will help enormously.
Plus, that's one toon who will not need to buy skills as they level up.
RAF ends at 60, so even if your previous main quit warcraft prior to tBC expansion, your old main is at the correct level (or higher) to join your team once RAF expires.
The big assumption here, is that the original account contains at least one toon who would fit into your team at end-game.

With a 60+ toon doing all of the killing, your RAF toons can blow through quests incredibly quickly. That's 3x the normal exp's for the quests.
You can also run a lot of instances in a short period of time, as you go higher level this slows dramatically for non-AoE classes, but is still a quick way to level and an easy way to gear the new toons.