Well I think your username says it all - Rokablly - it must be creature or otherwise you should have named yourself Kingofpain
But seriously, I think you can't go wrong on both. Not to compare... both great machines, I have a Creature, no MM, but I played MM a lot. MM is really different with the toys (castle, trolls, dragon) and multiball modes, Creature is a more nostalgic pinball, just a lot of ramps and shots. No bashtoys, just shots to be made.
If you only have limited place and cash consider this:
MM is a fun machine but pricewise very hard to get for the price a nice Creature goes. In that way I think Creature is a grow diamond. There will be more MM's on the market within time as MMR can still be bought. There will be no more Creatures, some may get a second life and be restored and saved from the trash, but the amount is Creatures is fixed.