What now?

I'm in the middle of a transition week and this is a good time to reflect upon what to consentrate on further on when it comes to main targets. My preferance when it comes to sport is decided earlier on-running. My thoughts now are on what field in running I should consentrate on. It's clear that long-distance running is my main field, but there are different ways here to choose from. Marathon has been a good choise for me about half a dousin times, but I'm not so certain any more about that. Having runned a couple of Ultras this quarter I've experienced a greater pleasure in doing that than marathons. Why then should I spend any more time on marathons?
Frankly I don't know. Why should I? Maybe I'll just call it a day when it comes to marathons and consentrate completely on ultras? Why not if that's what I like best and what's works best for me?