Honestly Yuri would have been ok but he has many flaws
1. If truly he loved her and actually thought of her as a person be would tell her keifers plan
2. He wouldn't bother proposing to her or agreeing to the talk of a wedding in the first place when he knows she likes keifer and wouldn't truly be happy with him
3. He has low self esteem am not going to lie and is probably too scared to go for what he wants only going when he realizes that he probably won't win
4. He just has this toxic vibe
5. You can never really tell what he is thinking which is not always good
And for keifer if you really think about it the only flaw he has is the stupid plan he came up with if he didn't have that plan I'm very sure a lot of you would have picked keifer....and also I don't even think Jay Jay has feelings for him she is probably just attracted to him and nothing more if you notice the attraction came when Yuri told her how he felt...in a way it's just basic attraction and she doesn't really like him...meanwhile with keifer from the first time she saw him she felt sometimes for him...
And besides at least keifer knows what he wants and just goes for it instead of just watching from the background.