Was looking at the ultimate edition on Amazon and was wondering if should buy it, or wait till October.

If there wasn't enough incentive for you to jump in before now, you might as well wait.

If you have the spare cash one incentive for at least picking up a used copy is you will get rewarded in Forza 4 for some aspects of your progress in Forza 3 like the cars in your garage. I would imagine a used copy is pretty cheap.

The Ultimate Edition is very affordable, you'll still really enjoy the Forza 3 experience until 4 comes out. I believe the new game loses access to Porsche vehicles too, so you can you get your fix in 3.

plus there is an achievement in Forza 4 for importing your save from 3 (or something to that effect)

I restarted my FZ3 just to beat it before 4 comes out.

I doubt the game is going to change that much between the two games. You might as well get the Forza 3 ultimate edition. Plus, I think Forza 4 allows you to transfer your garage or something like that from 3. The only thing I dont like about 3 is the difficulty. Not that the game is too hard or too easy, but I feel like there should be a difficulty for the AI between normal and hard (or medium and hard, or whatever the medium difficulty is called).

Forget about both. Buy Forza 2.

I went ahead and purchased the Ultimate Edition of 3. Really enjoying it so far. And the loss of the Porsche license is kind of a big deal to me, so this game rectifies that. 

Forza 3's great while it lasts, there is one achievement which involves getting top marks on all events; all well and good until you see what an undertaking that is - I've been playing it off and on since its release and I don't even think I'm halfway through those events, eventually there's a lot of track deja vu. The Ultimate Edition should include the fantastic Fujimi Kaido track though, definite favourite of mine. Definitely looking forward to Forza 4, I only hope they've made the career mode a bit less punishing for completists.

@pickassoreborn said:

Forza 3's great while it lasts, there is one achievement which involves getting top marks on all events; all well and good until you see what an undertaking that is - I've been playing it off and on since its release and I don't even think I'm halfway through those events, eventually there's a lot of track deja vu. The Ultimate Edition should include the fantastic Fujimi Kaido track though, definite favourite of mine. Definitely looking forward to Forza 4, I only hope they've made the career mode a bit less punishing for completists.

Based on the achievement list that's been out there, not even close. In fact, it's probably twice as hard now. Not only is the "gold on all events" thing still there, but now they've got a few achievements that will require you to have millions and millions of credits and own lots of very very expensive cars.