SP303 vs 404 vs 505

i'd suggest 404SX or 505 outta the ones you've mentioned if you're looking to use them without the mpc

SX over the 404 og as you can copy patterns easily, and the machine generally runs alot quicker than the 303

505 is dope too (same sound engine as the 303 but with a screen, the autochop is hit 'n miss and a bit slower in operation)