Köln or Paris?

My favourite band is going to tour again in the spring, but so far there are no concerts planned in Belgium or The Netherlands. So my BF and I decided to book a trip to either Köln or Paris to go and see them when there aren't more dates announced in March. I know that Köln is cheaper then Paris, both in getting there as in hotels, but to be honest, Germany doesn't interest me as much as Paris and I know Paris a little bit since I've been there before. Since we will only be there for a very limited timed time I think that is handy, so I can show my BF around. Instead of going by train to Paris, I was considering going by bus because it is less expensive BUT it takes a lot longer. Another advantage to Paris: my BF speaks a bit French (better as me!).

Aaagh doubts... someone has some advice?