The first one is allways the most memorable, be patient! There are plenty of cabs for sale out there and rushing can lead you into a heap of reopairs you don;t want to be left with making your arcade experience bothersome.
Like said above monitor is allways the thing to look for, but keep in mind the body of the cab, not necessarily the paint or mint factor of it, but more like the shape. There are plenty of "behemoth" cabs that belong in a fire pit, many woodworkers back then could care less for practical designs and only few cabs had a nice cut for their profiles.
US MVS cabs are a testament to excellent wood design, there are other very nice cabs like the Midway ones with very comfortable CP's, and better yet the revered rotable dynamo cabs, man those are nice for all jamma purposes. Some capcom cabs are nice, and very ilttle namco cabs are nice at less they are dynamo conversions, so be weary, but most of all be patient, the cab market is inflated with sellers not much for buyers right now.
Another cab worth mentioning is the Sega Titan ST-V US cab, the only plastic US cab you'll ever see, pretty nifty for a conversion, but unfortunately it is not rotable, big cab though, but it compensates with lots of elbow room and elegant curves.