I have both games in my collection. My MET is a Premium DD, but the comparison is still easy.
TZ is a classic game. Amazing theme implementation. Beautiful 90s machine.
However, I would take MET all day and every day over TZ. It just suits my style of play much better.
You have to figure out what you like about games to make this decision. If you like Multiballs, speed and flow, then it's MET all the way.
If you like mechanisms, and interesting gadgets, and don't mind stop and start, TZ is a masterpiece.
Play both as much as you can before you make a decision. You can't go wrong with either of these machine... unless you choose TZ over MET.