Sigma are very good as well; my only gripe is the smaller harness input rather than standard JAMMA size. Not a huge problem, but it means if you can't make your own then you have to hunt one down. I really like that Sigma boxes can do composite and S-Video in addition to RGB meaning any old CRT will do. The DIN13 plugs are a little annoying, but it's super easy to make adapters using MIDI DIN13 cables and DB15 breakouts. Of course, we're starting to get into non-beginner friendly territory here with that, so if going the Sigma route it's probably best to get something like the Raijin with controls built in or an AV series box with matching controllers.
Example of the adapter below being used with my Sigma 1AV; I have the matching Sigma 3TB controllers too, but to use a (AV-5000 use) DB15 Mahjong controller or my DB15 equipped main stick I needed to make one.