Striker would be awesome as you get to score many goals, but I think attacking mid is also awesome with the responsibility it has, passing to set others up, controlling the game. However, if I were to play seriously, I think I would be best at fullback or defensive midfield. Primarily making tackles while also supporting the attack is where I think I would enjoy the most.
I'll do my scenario by country/region:
Spain: Valencia or Malaga
England: Arsenal
Italy: Inter
Germany: I have to agree with Dortmund
Americas: Boca Juniors God damnit!!!!!!!
Though if money weren't an issue, I would say Boca for sure...as the enganche/CAM. That is the dream scenario.