i would suggest a combi pack.

5 X class type is our "easy mode" fairly simple macro setting ect (ofcause you can get complicated and do alot of stuff if you like )

so try
1 X class + 4 X class
1 X class tank, 1 x class healer, 3 x DPS
ect
make it more challenging and see how you do (ofcause it all depend on what you find fun )

"fun" groups
5 X Hunter, also knowned to the world as the 10 man group
1 x priest, 4 X Warlock, I is dying to try this myself as i use to play an afflic warlock and cant wait to try out 4 of them (and ofcause 4 felguard should be tried too)
5 X paladin, wierd combo for me. but i could see the fun and also a big challenge with alot of melee but im guessing there is some AOE dmg in this group with Consencrate and some burst with "Angel Wings" + stun + seal of command and a crusader strike x nr. of retri.
5 x mage or the 1 x priest, 4 x mage, Similar to the warlock group but bigger burst dmg imo and better AOE possiblities, but less survivability because of no tank and cloth.
5 X druid, "What is natur's call?" the person screaming when 5 moonkins are showing him the nice lightshow of moonfire. if you ever get tired of running instances, doing quests, Then there is always the option of making a Dance group.

so Fun is in the eye of the beholder (better run before the beholder gets him out of there because it is gonna be mad).
but there was a few suggestion, and a few repeats from earlier posts