Who should I manager leverkusen or Juventus??
depends on transfers cos in the Italian league you can only sign 2 foreign players
leverkusen, its a harder challenge than juve.
I've had a Leverkusen career go very well on FM11, fwiw. I've always felt having a large stadium at your disposal is a big advantage, Juve win easily in that regard, but just as a data point, in my Leverkusen experience they expended for me, then built a new stadium, then expanded that - all rather quickly, and all without my ever having to ask. Whether that experience would be repeated is of course unknown, but it seems to be a club with a lot of upside if led well.
The German league is more competitive imo but u could make Juve THE European powerhouse!