If the team you level to 60th is horde on earthen ring.
Then the levels they grant, will be to horde toons on earthen ring.
You need to physically target with the granting toon.

If you want both factions, RAF is still the time to level toons.
Doesn't matter if they're the same or different factions.
Now is the time to level toons from 1st to 60th.

If you have a higher level existing toon to boost with.
I'd consider boosting one faction until your satisfied.
Then faction transfer the booster to the other faction.
The faction transfer lets you bring gold with the toon, which will help starting a new faction dramatically.
And boost teams there too.

Once you're done boosting, do all the granting levels on both sides.
Be sure to grant levels before RAF expires.