Total Nuclear Annihilation or Houdini would get my money first.

We will have both games side by side at the European Pinball Championship in Boras, Sweden this week end. I had the privilege to play both games in succession for a couple of hours.

In terms of theme... Alien of course. The video clips are well integrated. The bumpers are really cool. The Xenomorph is a really nice toy.

In terms of shot map... it's not even close; DI has one of the best layouts ever designed - really.

DI has flow, Alien has flaws. Some of them can be addressed (very poor lighting of the lower area; a few bugs; Alien's lower right flipper was a bit weak, game is much slower than Full throttle, etc...), some won't be easy - feeding the upper flipper for example.

You really have to play both games before deciding. As a player, my choice would be DI without hesitation.

Just a follow-up: I could play Alien again the next day. Some of the issues (weaker flipper for instance) were solved. It played better. Only one bug during multiball (one ball would not launch)
I still prefer DI, but but not by the huge margin I described the day before. Alien has a relatively slow learning curve and some interesting rules. Solving poor GI illumination of the lower PF should be easy.