I'm rarely interested in triangles, but - like pretty much any literary plot device - it all comes down for me to the specific characters involved. Every case depends entirely on its own merits, therefore...

With the second question, seeing as we're talking fiction, any of the answers can be satisfactory in a literary sense (even the ones that I really dislike - if it works for the characters and the time and place, I'd rather that than a resolution I would like in real life but which doesn't work in the specific story). Likewise, every one of them can be ghastly if they feel imposed...