I would suggest you get couple cans of sealant foam to seal any cracks and gaps. Spend the extra money and get the cans that go on the gun(i think they have them at homedepot now), instead of the cans with the straw. Using the cans with the straw will just make a mess and be frustrating.
If your not going to be heating/cooling it all the time i would go with fiberglass and use R13 unfaced (no paper on the batts) then cover it with 6mil poly. Its a little easier if your not used to putting up batts and the poly will help seal the walls up better then the paper. And probably an R30 in the ceiling, depending on how its framed and if your doing a flat ceiling or the rafters. And when doing the batts take your time and cut them to go around any wires in the bays, (something your supposed to do but most insulators dont due to time it takes.)
If you were going to heat/cool it fulltime and spend alot of time out there, you could find some one local that does blow in cellulose insulation. It would make it a more comfortable building (sound proofing, less drafts and mold, bugs, pest, fire resistant) but it would cost a bit more. You would save on engery bills but in a building that size how much would depend on the garage door.