Gunther.
As an oldster, I just can't imagine marrying such kids like
Sam,
Alex,
Haley or
Abigail (though I like them very much).
Elliott is a snob. I like dandies, but not really as a husband.
Harvey is mature, okay, but there's just nothing attractive about him for me.
I relate mostly to
Emily,
Leah and
Sebastian, had even married Emily and Sebastian, but the latter is still as immature as the other boys, and Emily was a bit of a disappointment in married life.
I really like all of them, even or especially
Shane, but as friends, not as spouses, and Shane always seems kind of unkempt. I'm sure he doesn't smell good.
Maru - yeah, she's okay.
But
Gunther! He's mysterious, and he's damn good looking. I remember my frustration in my very first save when I realised that he's not a marriage candidate, not even an NPC you can interact with or befriend.