It varies per person on their favourite romance.
for me, it's obviously between this breton and Muiri
it was love at first sight. for the breton ofcourse.
the wonderful tales starts off when she asks him to kill her ex-boyfriend, and by golly the Breton accepted, traveling to Windhelm by a carriage and showly tracking his way to a old fort where the ex-boyfriend was waiting.
using stealth and the Breton's jolly faithful bow. he kills all the guards and the ex-boyfriend.
upon his return she is delighted. and gives him his reward... 500 gold peices.
2 days later the breton appears with a amulet of mara, Muiri notices. and the Breton then asks her to marry him, she said yes.
He then travels to riften to ask the priest at the temple of mara to hold a wedding. the date was set.... any time the next day between 6 am and 6pm.
he arrives at exactly 6am on the dot. they are married happily ever after (500+ days)
Ofcourse i'm just talking about my skyrim character and the fact you can only marry her by joining the dark brotherhood (assassins) and killing her bandit "ex-boyfriend"
BIG OT POST SORRY!
(i am not sorry)