First of all, I would suggest that you try and learn to pick locks from sources other than "Easy Pickings". When I originally started lock picking, I got the same set as you (Assuming you've got the Southord 5 piece pickset w/ easy pickings). I found that book extremely unhelpful, so my suggestion would be to look around on this forum, as there is some excellent info to help you get started.
As for what lock would be easier for you to start with, most Masterlocks are quite easy to pick, however the diffuculty depends greatly on the model. Somewhere on the Masterlock, there should be a lock number. Check this number against Shrubs Masterlock chart at
viewtopic.php?f=9&t=23712. Generally, the lower the lock #, the easier the lock will be to open. If there are no security pins, and there are a few amount of pins in the Masterlock that you have, then it is *probably* a good and easy lock to start with.