Yea, they are sooooo different. Kel gave a great breakdown of the main things they are both best at.
I have the 404sx & 500, I love them both, but if I had to choose...I would go with the 404 (I hear the 404 og has better vinyl sim, a lot of people would say go 404 og, I've never used it, but really happy with the sx).
Also with the 500 you have to be careful. People have a lot of issues with them. I have a few issues with mine & I paid $400 (it's mint, fat pads, extended memory & I had a 30 return period, I wanted to reduce risk). Every time I create a new program, reverb is automatically assigned to every sample, which the 500 can't handle, so instead of hearing reverb, all samples only play in the left side & the right side is all distorted. I just remove the reverb, but the point is it can have odd behavior.
Also with the 500, you have to sample in mono to get the most out of it (the same kind of goes with the sp404 due to polyphony, but resampling with either can help with this). When I sample in stereo with the 500, only 3, maybe 4 sounds can play at the same time & effects can't be added (I'll lay down drums, melody & bass, which is the most I have been able to use in 1 beat when sampling in stereo & can't use effects). It's supposed to have the same polyphony as the 1000 & 2500 (32 polyphony), but I can push the 1000 & 2500 FAR, waaaaaaaaaay farther than the 500. I still love it, it's an MPC the size of an ipad & it's great for hip hop/boom bap beats. I just want to point out a few negatives.
I got the 500 to use WITH the 404sx. Together they make an amazing portable pair. 500 for it's great sequencer & the 404sx for it's effects & memory. But then you're paying $700 - $800 (could probably get a better deal). Worth it in my opinion tho, the possibilities with the 2 are limitless & they're small enough to take with you everywhere.
I know everyone is different, but I also feel it's safe to say you can make beats "easier" on the 500. I'm not sure if it chops tighter or if it's sequencer is just tighter, but it took me awhile before I could make decent beats on the 404sx sequencer. The first year I just made beats in resample mode. But once I got the hang of the sequencer & combined it with resampling... WOOO!
You should check out some of the sp battles in the arena, listen to what can be accomplished using nothing but an sp. If you want to gain skill, I gained the most skill using the 404sx out of all my gear. And once you overcome challenges with it, it is a great feeling
My opinion would be get the sp404......save money.......then get the MPC 1000 with JJOS. If you find making beats on the 404 too difficult you can at least use it for sound design & performance effects with your ABleton beats. But this is an opinion, if you don't like the process or the workflow of either it won't work out.
In terms of portability they are almost the exact same size, if I HAD to choose, the MPC 500 seems a little smaller, lighter & doesn't have knobs that poke out (lost 2 knobs off the 404 pretty fast taking it everywhere with me, all tho replacement knobs are cheap). But both are close to equal when it comes to portability.
Oh & I forgot to add, the 500 starts to whine like a little bitch when it's batteries get low. At least mine does & others have said theirs whine's all the time with batteries. So I change out batteries sooner than needed due to it's whining (meaning the 404 lasts longer on batteries for me).
