To start with, let me assure you that MoW is a very unique game, which can be very much enjoyed. You would either love it or hate it, there is no middle ground.
I would advice you to play MoW and AS demos to find out which one is for you. You might find out that the single player is different in both games. For me, MoW missions win, coz they are very well designed and not as samey as the skirmish missions. You can find out more skirmish missions here:
http://www.digitalmindsoft.eu/forums...p?f=148&t=9105
Also watch out for performance issues in AS, esp. if you are an ATI user. Your AS demo experience will tell you if the game will be smooth or not for you.
Both games have interesting MP and pretty big MP community. AS introduces lots of changes into MP, but it doesn’t revolutionize it. As long as you play with the right settings and with the right players, I am sure you should have a blast in both MP.