I would like to use the Wico 2 1/4" trackball on my first MAME cabinet.  I have two questions and would appreciate any feedback..
1. What is the difference between the "Active High" and "Active Low" model trackball?  Which should I get if I am using an Optipac?
Both work with optipac; you just change a jumper on the optipac board.  IIRC, all the new 3" are active LOW, so you might want that model 2 1/4".  But does not matter, really.
2. I am choosing the Wico trackball over the Happs Model mainly due to price (about $60 less).  Is the Wico similar in performance to the Happs, or is it definetely not the same quality / feel as the more expensive Happs?
I don't have a 2 1/4" happs, but the wico 2 1/4" is solid arcade quality.   (BTW, Wico and Suzo 2 1/4" trackballs are the same thing.)  Someone who has tried both will know more, though.