If I was starting over, and only had an investment of one toon per account...
I'd probably ditch four of the accounts, pick up four new ones and go with RAF.
A > B > C
A > D > E
Possibly transfer a character, from the existing accounts if they're leveled/geared enough...

Assuming you set up RAF, or decide not to...




You'd want to get your toons into a Level 25 guild, for the perks.
Or baring that, the highest guild you can join on the server.

You'd also probably want to be on a server with other boxers.
Since you don't have much investment on the current server.



I would probably level either Feral Druids or Paladins.
Because 5x the same is easier than a mixed team.

And either group includes both a Tank, Healer and DPS toons...
Which allows you to run instances for gearing and the accrual of Justice points to buy heirlooms with.
Just because you don't start with heirlooms doesn't mean it isn't worth a week or so of running instances to get a full set.
I'd likely get the Cloth pieces with +Experience, because any toon can wear them and honestly 5x Warriors totally in cloth and using a weapon from 20 levels back... will still quest just fine.

With RAF, the fastest way to level a team is to boost them.
So boosting is going to be the fastest method, without RAF as well.
It's just other methods will be a lot closer than before...
Example...
Speed is 100 when Boosting = 300 with RAF.
Speed is 80 when Questing = 240 with RAF.
If Boosting is the number 1 method and Questing is the number 2 method, the relative order of the most efficient leveling techniques is not going to change.

So my goal, after heirlooms will be to have a strong booster (Prot or Ret Paladin, Feral Druid), to boost other teams with.

I'd probably create all the teams and log them in.
Just so they begin to collect rested experience.

And if I knew I wanted "x" teams, bounce between them to optimize the use of the Rested experience.




I'm personally enjoying...
- 5x Druids, both as Feral and Resto.
- 4x Frost Death Knights, with 1x Holy Paladin.

I'm leveling, for MoP:
- 5x Paladins, which will dual spec Ret and Holy.
- Will likely run 4x Ret, with 1x Death Knight.

I'm tempted to level my Warlocks (20ish now).
- 4x Warlocks and 1x Priest.

In the past, I've liked:
- Paladin Tank, 3x Elemental Shaman, 1x Warlock
... but toons have moved to other teams, and the Pally is actually on another server (The Zerg) as a Healer now...

Beyond that, I have:
- 5x Priest
- 5x Hunter
- Mix: Blood DK, Disc Priest, Elem Shaman, Destro Lock, Arcane Mage.
- 3x Elemental Shaman, 1x Elemental & Resto Shaman, 1x Boomkin and Feral (will be Guardian in MoP) Druid.

... Plus others that are there purely because they're high enough for tradeskills.
... And others, who are purely bankers... seven guild banks currently.