Go with the Spit to start ......... but then again everything else will be a disappointment after that 

I have them both. Personally I find myself flying the Mustang more than the Spitfire. Not quite sure why. It just gives me a better feeling. I like the engine sounds better in the Mustang, and the startup and landing sounds are much better in my opinion.

When flying the Spitfire I usually have the 'real view' feature turned way down or off. I find it a little bit distracting.

One nice feature about the Spitfire is that if you run the engine full bore for more than a few minutes, it will detonate resulting in a windscreen full of oil and black smoke streaming. You will now be flying a glider. I like that kind of realism.

I also have the WOP P-47. It is also one awesome airplane. It has the best big beefy radial sound I've ever heard in FS9. Flies real steady and is wonderful for terrain flying.

What I'm looking forward to now is the release of the Maam Sim TBM Avenger. I have their B-25 Briefing Time and the level of detail is unsurpassed.

I can't speak much for either the spit or the stang.  But, I can speak for the Shockwave product I do own, Wings of Power.  If those bombers and German wonder planes are to be taken as an example then I  would be suprised if anyone could make a WW2 fighter better than Shockwave.  I would go for the M ustang first simply on the strength of what they did with Wings of Power.  I also own "Breifing Time" as freedspeak mentioned.  Yes, that B-25 is awesome, the best sim bomber ever, of course that is because they had the real plane right at their fingertips during design, does make a difference.  But, Shockwave came very close, as far as best sim bombers.  Very very close.  If they can do that with bombers, fighter should be a breeze.