I know this is an old thread but it's one of the most useful post I found when I did a Google search so I wanted to add to it.

A > B > C > D > E
Pros
You can end up with high level characters on B and C.
Over all, gifts the most levels
Cons
The level that are given are spread out in places where they might not be useful
Of all the options this gives the least levels to your main account


A > B > D
A > C > E
Pros
Gives the most levels to your main account.
Cons
Not many levels given in total, very few given to any other account.


A > B > C
B > D
B > E
Pros
Gives a high number of levels to the main account. (not quite the most)
Gives nice number of levels to the 'B' account
Cons
Does not give any levels to 3 of the accounts.


I think the 3ed option is the best. If you set it up so C,D,E are your DPS then it gives you options for your tank and healer. And it gives you a lot of characters on your main account so if you stop multiboxing you are still left with high level characters.

I made a spreadsheet to work out what I would need to level. My main account already has some high level alts and I planned on power levelling an 85 and 22 character. Then this is what I get before and after gifting levels:

using A>B>C>D>E
A 90 80 70 6 -> 90 85 85 85
B 85 22 1 1 -> 85 85 31 1
C 85 22 1 1 -> 85 85 18 1
D 85 22 1 1 -> 85 64 12 1
F 85 22 1 1 -> 85 22 1 1

using A>B>D, A>C>E
A 90 80 70 6 -> 85 85 85 85 62
B 85 22 1 1 -> 85 64 12 1
C 85 22 1 1 -> 85 64 12 1
D 85 22 1 1 -> 85 22 1 1
E 85 22 1 1 -> 85 22 1 1

using A>B>C, B>D, B>E
A 90 80 70 6 -> 90 85 85 85 34
B 85 22 1 1 -> 85 85 85 13
C 85 22 1 1 -> 85 22 1 1
D 85 22 1 1 -> 85 22 1 1
E 85 22 1 1 -> 85 22 1 1