I left off on the ASR, to sum things up short I would say it's a good tool especial for those that are more musically inclined, it just falls short a few points on user friendlyness for me especially with that small ass viewing area doesn't help much. This unit may be best suited as an add on to an existing system or as a midi-controller. Now for the MPC-2000, ummm-hmmm. To start it has 64 midi-tracks, a user friendly control area, easy viewing window, edits samples via waveforms, and the list goes on. My only gripe is with expansion of the unit..it can be freakin' costly. If you look to add an F/X board, or whatever you could be spending any where from $299(US) and up, not a good thing if you're on a budget. Most people that I've met use the MPC as the "Master Control" for their set-ups when it comes to doing midi work. Also one thing that's a pain is having to "load" the unit each time you power up. Unless you have things on ZIP drive it makes things less painful. As for the Yamaha SU-700 for the features and ease of use, I give this a thumbs up. It give you around 48 midi tracks, F/X filters, and has a looping function that is about the simplest yet. For the interface...it's so simple a child could use it, everything is pretty much mapped out in front of you so all you have to do is "connect the dots" to get things happening. It's also excellent if your a DJ and you're looking to incorporate a sampler in your set-up be it in studio or live.
As for me I opted not to get a sampler at all at least not now. I'm going to invest in the Cubase VST/Studio Pack w/LM-4 & Pro-5 modules, if you're into computer based recording this product and it's VST plug-ins will cause you sonic-wet dreams (if there is such a thing).