Apparently Asche has tried 2B and it was about as good as when Utley tried 3B. AKA really really bad.
Catcher is a real tough position to learn with more chances at getting hurt, whether it be concussions or knee or hip issues. I'd probably try outfield before catcher. But really I think it's either 3B or 1B for Franco. If you want someone to move positions, it should be Asche. Franco is simply more valuable and has a much higher ceiling. Plus, Asche has said he will try any position to remain in the big leagues. I think Franco will be ready to come up by mid next season. If you want to keep Asche, I think trying him at outfield in spring training would be the best bet.
Franco is too slow for the OF, so yeah it's 1st or 3rd. He has the tools to be a catcher, but to move him this late in his development would be a tough thing. And it would probably delay his arrival to the majors by two years.
As for Asche, I think we're all comparing his 3B play to Michael Young, so yeah he looks like Brooks Robinson out there. Questions about Asche's defense followed him through the minors, and although he's improved I'm not sold that he's an above average 3B defensively. I'm also not sure that his bat looks that good in left or right field.
I agree about Franco having the higher ceiling. He's not as athletic as Asche but he has a better arm and maybe better reflexes at 3B. And he has a better chance at being an impact bat. I could see Asche in the OF or Franco at 1B for a little while, just to let them both play, but I don't see it happening long-term.