please help a newbie decide

[foxhands]

so i've been creating loop based music for several years and am finally looking to get a sampler so as to make live performance of songs simpler.
a friend has the sp-555 and so i've been trying to compare that with the 404sx - my question is, can someone here tell me the fundamental differences between the units? how many samples can play simultaneously on the 404 compared to the 555? is there a length limit to how long a loop can be? i am totally new to this and just stumbled onto this forum, so any help anyone could give would be greatly appreciated!

[shmedy]

i have the 555 and im very partial to it. so remember that as you read this. the 16 pads of the 555 make a big difference to me because i like to chop up beats by the 16ths. the looper is also pretty handy for many things. does the 404sx have usb? im not sure, but if it doesnt the 555 definately excels there because you can use it as a sound card for your computer. you can record sounds to your computer through the 555, or sample sounds from your computer directly to the 555. so the usb is pretty important.
as far as memory i think i remember the 404sx having more but im not sure on this also? but i am sure that i never have run out of memory on my 555's 2 gig cards. so hope this helps.
oh and of course the 404 is portable(battery operatable) if that matters to you.