Adam Warlock. Not sure what exactly, but there's a whole universe out there for him to explore. Love his supporting cast over the years, love Marvel Cosmic in general, and love the character. His evolution into a magical being would lay the groundwork for interaction with Doctor Strange and the like as well. Plenty of places to go with Warlock, the only problem would be the general comic buying public not liking him as much as I do (and the fact that I've never written anything for mass consumption and I'd probably be terrible at it, despite how much I love comics in general and Warlock in particular).