What kind of money are you looking to spend? How important is an F attachment to you? Does it have to be a new horn or would you consider a used one? Are you planning on majoring in music? What are you playing on now? What don't you like about it?
This could help narrow things down. In a perfect world where money is no object, we'd all ideally own a few horns. But it sounds to me like at least for now, a medium bore horn (at biggest) would be the way to go, because if its versatility.
But answer my questions and maybe we can help more.