It depends on how you get along in each situation. Do you have much experience tandeming? If not, there could be stress between you. The same goes for riding distance on singles. If you don't have much experience tandeming, are you adaptable, or does one or both of you get grumpy when challenges present themselves? Which kind of bike do you think will present those challenges? I got our tandem to even out our differences in abilities, and it does that, but it presents different kinds of challenges.