My CJV150 prints very well, I couldn't be happier with it. It does everything from extremely good quality 3x3" laptop decals to 2 pass 360 dpi banners, cutter is super precise, I have mine set up with 8 colors.
Mimaki pros:
Cheaper ink ($75 vs $105)
Comes with a take up unit and ink set
Sheet cut function is fast and leaves clean cut line (doesn't seems to be a biggie but on Roland you'll cut off the sheet manually I guarantee)
Roller pressure can be adjusted so you'll have no marks on print
640i is discontinued
Roland pros:
Versaworks is really userfriendly (mimaki's rasterlink is ugly, crowded, unlogical and freezes a lot of times, real pain in the A, print time estimation is way off - wonder if ink estimation is accurate? )
Roland can kiss cut AND perf cut one after another. Mimaki can kiss cut OR half cut but not both.
Both machines are designed in Japan, you cannot go wrong with either one, you should choose the one with a closer dealer to you.
Oh, and one more thing - although the printheads are the same, roland charges $3000 to change it and mimaki charges $2500