IDX was great 20 years ago, then I couldn't get them repaired properly. Microcoin QL also used to be excellent, but the new ones I bought about four years ago have all been jamming frequently for no obvious reason, and the plastic frame parts are all broken because people will beat on them. If you go with Slugbuster, you might as well get the III. The PEM-55 (2
coin model) will take a dollar
coin and only give a quarter credit, and there's nothing you can do about it except have the
coin slot too small to fit a dollar
coin.
I do know a guy who upgraded his two car washes and put in all IDX MA-850 and he hasn't had any trouble with them. I don't know what their repair system is like, but it used to be so bad that sometimes units would just not come back with "Beyond repair" written on the invoice (These were not damaged) or a brand new one that wouldn't work out of the box, sent in for warranty and came back with a note "No problem found" and still wouldn't work. This was with the older MA-800 models.
FWIW I tried one SecureCoin and really liked it, so I ordered two more. Neither one of those works properly.