You can still play the free version at the App Store just to test it out, there's plenty of great reviews
I have all 3 games and I would say that HAWX is awesome. In fact, it's the game that got me into these flight "sim" kinda games. As an added bonus, it's the only one with a virtual joystick, so you can play it at those times where an accelerometer is just useless. On the other hand, I think I'm getting the most gameplay from Ace Combat. I don't know what it is, but I find the gameplay in that one to be most appealing. It's definetly lacking some content, but what is there is awesome. If it had the level of content that HAWX does, I'd recommend that one more. FAST is great too, and it's free to try. On top of that, it's the only one with online multiplayer. It's the cheapest of the 3 too, at a small in game purchase of $0.99. The gameplay is pretty cool too, and they've recently added a campaign mode to make the game that much more interesting. The biggest money spender is the extra planes though. There are 3 other planes you can buy, and they actually look pretty cool and have decent stats. I'll let you judge from this post, as everyone has their own opinions about what they want. Don't forget to watch gameplay videos and read more than one review, as one reviewer could love a game and another could hate it.
In FAST (upgraded) you unlock at least 5-6 planes as part of the game. There are just other additional plane purchases available. You still get plenty of variety of planes without paying for them.
