I will be lvling both.. I for some reason never lvld a mage.. and have been regretting it every single day :S so 5 at a time is going to be a lot of fun ^^
the reason I'm sticking to shammies atm is that they simply have soo much versatility even though they have no CC and limited snares.

5x mage.. fun factor multiplied.. however be ready for some frustration with the micromanagement
5x shaman.. might not be as fun as mages, when it comes to spell choice, blinking etc.. but in such a group you have huge survivability, that the frustration you will likely suffer from running 5 mages will make up for the lesser amount of spells..
with this new tremor pulse if you time it right you should have one pulse going off every 0.6 seconds.. say byebye to running outside your totem range.. or if you prefer a little more mobility you can spread them out a little and drop them all simultaneously to cover a large area with antifear..

I want to experience both mind you

5x blast wave and 5x nova totem