I'd probably say a Paladin.
But any tanking class would work fairly well.
As would any AoE class that is capable of surviving and killing large pulls.

Any level 85 is going to boost through the Classic + Burning Crusade instances with ease.
Most likely any WotLK instances too.



Shammies make excellent outdoor boosters.

You need two toons to be boosted, because they have to be grouped.
Level 60's, can hit level 70 in a rather boring afternoon in Borean Tundra.

A mage or instant-cast AoE class as one of the lowbies is ideal.
Equip them with AH greens, only caring about Stamina nothing else.

Run around with the Shammies on auto follow.
Speccing one Resto for Earth Shield on the puller (lowbie) helps.

Have the lowbie tag a lot of mobs.
Then have all shammies (3 in my case, because I had 5 accounts) drop 3x Magma Totem.
Also drop 1x Stoneclaw for the Taunt + Stun.
As soon as Stoneclaw dies, have Shaman #2 drop theirs, ditto for Shammy #3 once #2 dies.

Totems are considered pets.
So pets don't reduce the experience a group takes, irregardless of the damage they deal provided the group has the mob tagged.
So you tag with lowbies, who are a group and not solo.
Which lets pets/totems do any amount of damage (97% maybe) and the lowbies get 100% of the experience.
(If a level 85 toon did the damage, again let's say 97% then the lowbies would split 3% of the mobs experience total).