I too think "3" is the best.
I've played them them all.
"1" was great for the time, good dogfighting and such.
CFS2 was great for adding content but somewhat lacked immersion as far as combat is concerned.
The boring CFS2 AI is legendary, LOL.
CFS3 came with a new format to allow for more objects being rendered at a time and to allow for a makeover of AI routines and multyplayer cheating, but was rushed out due to bizdev's christmas bussines deadline.
It has it's issues, performance wise but is to date the most immersive of the three - if you get it to run properly on your machine .
Ground pounding is excellent as a real war is going on down there, high altitude is great either as the both the terrain and the flightcode actually do work as opposed to "the other game you know which one"

The latest 1% creations shure have proofed that.
Beside, it's modeller's heaven, you can spend polygon budgets for a single plane that you'd otherwise use for 4-8 planes in any other sim.