Horses for Courses. I love flying the A2A Spitfire and the FSX-adapted English Electric Llightning in FSX. I love the air combat in CoD.
Right now I have to say the A2A FM and general feel is an easy winner. But it can't shoot down 109s
I use photo secenery in FSX with Autogenerated scenery off (trees, buildings etc). Above a couple of thousand feet you wouldn't know and I set Forest Off on CoD, it doesn't have any value except to allow targets to hide and I don't generally fight that low down anyway.