Avoid vertical microswitch pushbuttons. They tend to get "sticky". They would probably be fine for "incidental' buttons (power, esc, tab, etc.)
The horizontals are very superior. The horizontals also have a slightly softer spring, so they are easier to press (you can finess them better).
On the ultimarc site it says that their buttons use switches made by Honeywell, instead of those "cheap asian knockoffs" or some such. The switchs that Happ uses are made by Cherry in Mexico. I don't have any ultimarc switches yet, so I can't compare.
The main advantage of the ultimarc sticks is the built in restrictor plate, for that authentic 4-way feel, very important for 80s games like pac man, donkey kong, etc.
Bob