I rented from here in Puerto Pollenca
http://www.procyclehire.com/pch/bikes.htm
The Massi MTBs were OK. The forks were rubbish but everything else was fine. They will be able to advise at the shop on a few routes. I think the owners were English.
Land access is a bit hit and miss at that end of Mallorca. Big chunks of Land are owned privately and tracks on the map can come to end with big padlocked gates. There are maps available in Pollenca old town at the tourist information that have walking routes which had a lot of MTBers on them when I was there. If I went again I would probably rent a road bike as some of the road climbs were spectacular with miles of switch backs.