Marcurio was my first and as they say, you never forget your first.
I fell in love with his somewhat haughty yet goofy personality - his looks didn't hurt either. See, I fancy me some Imperial men, so marrying him was a given. It was great - until he glitched out and stopped cooking for me one day. He also does get much less talkative once you marry him, so that was indeed a let down. But I enjoyed my time with him in my first file ever, and I currently have him as my faithful steward in my Falkreath house.
My most current husband is Brynjolf (yay PC version!
), whom I married after the TG questline. Yeah, he's a modded husband, but I don't care - I've crushed on the man since my first playthrough of the TG storyline and he remains one of the very few Nords I find pretty damn hot. He's been a fairly constant follower as well, until recently when I took him back to the Guild. But since building my Hearthfire houses, he's been chilling at those, helping my stewards.
I was married to Mercer Frey for a very brief period of time, just for the epic lulz. But he was just so grouchy (unsurprisingly) that it really was hardly worth the ceremony. I did find it utterly hilarious though and still goof around in that file just spend time with him as my "husband". If I advanced the TG stuff in that file, there's no telling what would happen later as a result. Might blow up the game. One day I'll experiment!
Personally, I think Hadvar (and Ralof) should be marriageable by default. Seems to me like it just would make good sense, especially if you do the CW stuff to the end. One day, I think I'll mod myself a marriageable Hadvar because I now have the tools to use voodoo magic on all of the voice files.
Having perused this thread and others, I suppose I'm one of the odd women out since I have no real desire to marry Farkas or Vilkas. Farkas is sweet, but...I dunno. Currently scheming to make some of my own OCs marriageable soon as well, and play around in those files just 'cause.
Been curious to marry Cosnach, because Breton men are simply adorable, be they angry Thieves Guild leaders, hapless drunkards or anything and everything in between.