I was in your shoes this past fall. I ended up getting the 2008 Batman pin and it's been an amazing choice!
It will be a hard decision as all the new Stern tables have their ups and downs. I would suggest travelling if need be to a Playdium arcade etc that holds the new games so you can test each one out.
I can give you a couple up sides of a few new machines from my opinion.
Batman: Lots of close range target shots. It feels like a shorter play field when compared to Spiderman or Indy. The multiballs are nicely spread out with 3 different ways to obtain them. The artwork is fantasic both on the playfield and on the box itself. I've had mine for a few months now and certainly no complaints. The replay factor is very high!
Spiderman: I really liked this pin it's a faster play than the batman. It almost feels like they used a super wax finish on the playfield. The moving targets and lighting are second to none. I also liked the fact that they did not use voiceovers, either that or i could not tell. If you can afford the extra i'd strongly recommend the special edition. I played them both side by side for a few hours and the crome package and rumble pack really add to the value of the machine both visually and playing.
Pirates: This game has lots of nice distractions, ramps and etc. The boat that sinks iteself is a very nice addition. I found there to be a lot of replay value to this machine if you are a fan of the Pirates theme. The lighting and replay value is also fantastic.
Family Guy: A great theme, i am a fan of the movie series. This game has a lot packed into it. Almost crowded similar to the simpsons game. If you liked the Simpsons Pinball Party you will like this pin. The sound and voice in this pin really stand out.
Indy: This pin got a lot of flack i found. I find this pin to be a lot of fun. It's a lot of open holes to sink and a main target that drops a ton of pinballs once you hit the multiball. The sound and voice is amazing as is the fit and finish on the machine. This machine was actually my second choice. I am a fan of the series though.
I cannot recommend strongly enough to go out and play them. I travellled 4 hours from my home city so i could spend some time with these machines. It's a signifigant purchase so you want to make sure it's one that suites you!
Good luck!