I have a Hyper Neo Geo 64/ Super Neo 29 type II with a four slot - nothing better!
Of course cabs are definitely a matter of taste. I think the CP and easy front access on my Super Neo 29 is the best. I wish my Williams KI2 woody had front access for changing out games - its a real ass kicker to get to the back. Some people want a stand up cause its what they grew up playing, others want sit down (candy) so they can be comfortable - I went with one of each. Monitor size is another consideration my woody has a 25" and my candy has a 29" - but some think the 19" look best. Think about the features that you want most and then don't settle - cabs are generally harder to sell than to buy - so make sure you pick one that you want to hold on to. Same is true about condition. Pick one that you are happy with appearance-wise. If you don't you will spend more time working on it than playing it - its better to pay the money if you are picky like me...both my cabs are nice, but I think the only way I would have been happy is if I bought my cabs new.
I hope you find what you are looking for!