The one thing I would say is that you are likely to have a lot more opertunities to see Muse. I would try and see U2 before they disband or all become old men.
I'm surprised that they would play the same place on the same day. I would have thought that there was a fairly large joint fanbase. I mean, U2 (well... the Edge) even played with Muse at Glastonbury this year.
Also, I'm not the biggest fan of Muse. I don't think that they have any concept of subtlety or restraint. While I would be curious to see them live, but I don't think they are all that on record. I have heard that the Flaming Lips are just as good live, and imo, their music is a lot better.