I literally started doing this a couple weeks ago in my spare time.  The only locks I have is basically what is in my house, so I think the hardest lock I have picked was actually a Defiant deadbolt with one spool in it.  The padlocks I have are old and crappy from being used outside so those were a challenge to get past all the gunk, even after spraying them with lubricant.
Actually the hardest one was an Abus 85/40 which has a whole bunch of spool pins in it.  I didn't know it before i picked it, no wonder it took me so long, lol.