As others have said, if you want to talk on repeaters, you go with what's out there. Having dual band gives you more options. If your not using repeaters and just talking simplex there are a couple things to consider: what radios do the people you want to talk to use? I have found far more single band VHF (2m) than single band UHF (70cm). So VHF may score a win there. Next is propagation: both 2 and 70 are line of sight so, except in rare cases, you will be limited to local, however 70 supposedly penetrated buildings better that 2m (I only know that because it was a test question on the technician test.). So depending on your use, UHF may score a point. Next: there is more bandwidth, and in many areas less use in the 70cm spectrum. So if you are in a crowded area UHF may give you a better chance of finding unused frequencies. Finally, some people get dual bands specifically because they want to use cross band repeating.