I tried both before. Let's analyse the situation here :
- Fastred is obviously immature, but I don't like what her father is doing. He's trying to keep her in Ivarstead not because he's worried but because "we need to repopulate Ivarstead"? People need to do mistakes to find their own path. Also her mother wants to help them elope and I find it a little sad if you can do otherwise.
- Bassianus' main characteristic is to be unbearable. If you talk to him, he's rude and that's all. If you allow him to elope with Fastred he will wander in the market in Riften with or without her. Just wander. If you talk to him again, you will only hear about Ivarstead and what a pain in the ass you are for talking with him. So I wonder : what was his plan? Going to Riften then living in the streets? So much for improving their lives.
- Klimmek is a nice guy, I don't care about his knees. He obviously have feelings for Fastred even If he can't say it properly because Nords men are supposed to be tough (lol). So she left him for that and jumped on the next shiny thing (If I can say that). The thing is, if you really lost all interest in someone you won't come back to him thanks to a little persuasion. Fastred seems eager to take him back when he voice his interest, meaning Bassianus was probably a flirt.
Overall I find it more satisfying to go for Klimmek. As for your Stormcloack playthrough, I'd say Klimmek too because he's a local man with a simple life and he don't want to be anything else. He does manual, physical labor. To me, that's more like the ideal Nordic. Sorry for the big message about something so simple.