I didn't like Site 4 at all, it's considered to be a weaker game than Max Force.
I had an Area 51 Max Force for a while but it got very boring and I sold it. It's just endless shooting with end bosses and no storyline.
If you are going to get a gun game, I'd go with Jurassic Park Lost World, in the dedicated cabinet with the tube monitor. That game gets the most play out of any of my games at parties. The gun system can be a pain and be expensive to repair but if you look around and are patient the parts can be found on Ebay because I am seeing more and more of these being parted out.
With unliminted continues, it's not hard to go through the whole game, and it's not that long of a game either, but it's not easy to go through the game and be successful at every challenge. I've never done it.
I also believe you can swap in house of the dead II in this cabinet but I don't know if it's plug and play.