My curveball from a couple pages back: iRacing
3-way discussion?
GT5:
Amazing eye candy
a very nice career progression (can be enhanced through DLC)
An adequate online mode
Forza:
Good graphics (but the reflections are a tad much
A nice linear career, but there aren't special event types
TBH, i think Forza has the better sounds (more consistent good sounds)
iRacing:
The best racing sim physics. Period
A tiered license progression system.
An adequate way to match people by iRating
Safety Rating (though it seems to be useless with FastTrack now)
Most realistic damage in any sim. Period
Advanced mechanical failures
The tracks are laser scanned and continuously updated
The cars are laser scanned to have accurate aerodynamics modelling
While those are pros of iRacing, here are some cons.
The matchmaking system in iRacing reeks of Forza's hopper system
You have to pay 3 dollars every time you want to host your own custom session
Relatively expensive compared to the others, BUT is way cheaper than trying to go racing for real.
FastTrack lets a lot of unsafe drivers in fast cars by timetrialing like crazy
Damage, Tires, and Suspension modelling STILL need work
Sound needs work (this will be addressed in JAN)
Lack of cars, but Spec racing allows for even fields
Graphics are less than adequate by today's standards.
Aero modelling needs work on some cars.
Some other things that i cannot be bothered to mention.
Long story short:
EVERY sim, whether it be for console or PC, will have its shortcomings. There is no way to make the perfect sim.
My preference of the console sims? Gran Turismo 5
Why? It gives me an amazing feeling being able to drive cars that i would dream of even seeing IRL. Also, cars having somewhat accurate physics adds to the experience. Also, the customizable lobbies and lounges online adds to the Online mode a lot instead of just being thrown in with random people. Also, the game is $US60 and doesn't cost anything after that except for optional DLC (if it comes out). The online is free. I don't have to pay $60 a year (XBL) or $90 a year (iRacing) in order to keep enjoying GT5 online.
There's my reason. I know i went off topic with the iRacing comment, but it was to make a point that any sim will have its strong points and weak points. IMO, neither game is better than the other, but i prefer GT5 because i am a GT fan, it is the least expensive venture of the 3, and contains some of the most beautiful recreations of cars i have seen.
I own Forza 3 and an xBox. I can vouch that it is an amazingly fun game. They nailed the career mode. It is absolutely fantastic! I just haven't decided to play it because I have either been playing iRacing or GT5 and haven't bothered to renew my XBL Gold.
tl:dr
All racing sims have strong points and weak points. GT5 and Forza are both great games and IMO neither one is better than the other.