If Alien was built and supported by JJP, Stern or Spooky that would be my choice but Heighway is too much of a Trainwreck to consider buying a game from them right now.
Between the other 2 I have a decent amount of time on production games. Both are great games but for me TNA is the more addictive game and would be the one I'd be most interested in buying. It also helps that it's $1000 cheaper than Houdini too. Houdini is pretty packed and a better value than JJP or Stern LE/Premium games though. In a really small collection I'd probably go with Houdini but in a mid to large size collection I like the variety and fun that TNA brings.