I liked the STNG so much, I purchased 2 of them as long term keepers. I feel TAF gets a bit repetitive. If you have many machines, and only play a few games here n there, Addams Family would be worth a purchase as well, but to play it over n over n over again, its not as deep as the STNG.  Still, its still a great game, but i reckon 2nd to STNG.
 
* A few years ago, these Star Trek titles in great condition were alot harder to find, espescially Australian delivered. There are alot more around today, but be careful, do your homework, and buy a machine that comes from a private collection, versus a unshopped hugely used eurohack, unless u know how to replace colis, rebuild flippers, adjust optos, and strip the playfield fully for a good clean, rerubber and reglobe. $3500 for a nice STNG is fine. You always pay for quality.
Some people say that these STNG are nightmares to shop, but i disagree, they have no more basic desires than any other pin. If anything, they are a very solid machine. Cannons are a area for rebuild, but a very straight forward process etc.

You could consider purchasing a Data East Star Trek 25th as they are a great fun game as well. Find a ST25th and have a game, also lots of fun.
Dr Who, not bad at all, but you have to be a big Dr Who fan, otherwise, again it gets repetitive. Still a fun machine.

p.s - meet as many forum members as possible, visit n play some machines in collections, thats the best way to pick a real good title. Are u in melbourne ?