That's for you to decide, based on a number of parameters you aren't sharing.
What classes are your mains? What level will you keep said "alt" at?
Shamans get haste, clerics get res.
You can always level a "cleric" on the side, while your friend levels an "enchanter" on the side - or vise versa. Make them on different accounts and benefit equally from them. And later on realise you should bench your mains and play the enchanter/cleric duo instead
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