Best solo trip: There are some parts of the world that feel designed to be seen with someone, like Paris, and there're some parts of the world that are better seen by yourself. Latin America falls in the latter category: because it's mostly Spanish-speaking, you're forced to be open to the world and interact to the world around you, to bus drivers and the cafe owners and to the restaurant people - you're required by necessity to be more interactive. As opposed to when you travel with someone, when you're always speaking English to each other, and you're often facing each other as opposed to viewing what's around you. So I'd recommend Latin-America for a solo getaway. 

Winter vacation you'd recommend: Brazil. I really, really like Brazil. And it's warm there during our winter. The main problem with going there is this, however: the cool stuff is found in northern Brazil, but all international flights go south of Brazil, so you actually have to fly all the way down and come back up north. Still, that's where you should spend most of your time: it's really a fascinating place, it's where most of their colonial history, with its missionaries and slavery, took place. On that note, Brazil is interesting to compare to the United States, because it's probably, of all countries in the world, the one whose historical racial legacy is most like America. But they're much more obsessed with class than race, whereas America's much more obsessed with race than class. It's an interesting place to visit, I definitely recommend it.