Air,
Try the 770 out for a test run at a local music store if you can find it.I would recommend the 202 over the dr-5.
The dr-5 sounds are sort of chessy (my boy called it the video game beatbox)The cool thing about it is that you can write string lines,synths,drums..
The 202 sounds awesome! Straight up its just a better machine.It has the 303 sounds plus more.it also has delay/flange/chorus to make orginal sounds.Its mostly drum sounds.
go to
http://www.harmonycentral.com
the have a section called "user reviews"
this will give you an idea of what each does.
Peace!