All spouses have different dialog and some do unique things after marriage. Also some change their work schedules while others don't at all. As Filthy Gorilla said, each also has a different 14
events and Gifts, all of which are fun.
It may come down to how much you RPG the game. If you are looking for a functional addition to the game, Penny and Emily offer unique clothing and room decor options. If you're looking for useful Spouse Gifts, then Abby and Maru give Bombs. The rest give you things are common enough that you're probably not going to need them much. All give a different choice of cooked dishes so that's quite variable. IMO even the Bombs don't make much of a difference as you don't get gifts every day and then it's random from a choice out of about 10 things for what you get.
But I'm RPGing the game so I'm there for the spouse dialog and I find Emily and Haley to be the best for this. Abigail is pretty good too. Unfortunately I haven't played my Penny save for a long time but a few years ago her post-marriage dialog was only so-so, though more dialog has been added in newer game updates. I wasn't married to Maru long enough to get a good feel for her dialog, I should return to that playthrough. And Leah avoids me so I haven't married her yet. LOL she's probably more perceptive than the rest.
Back to the Work Schedule thing, Maru keeps her career as does Penny. Emily works as the Saloon only on occasion, helping out for old time's sake which I like. Abby doesn't wander as much as she used to which bugs me a bit. Haley also ends her aimlessness when becoming a Farm wife so you'll need to make peace with yourself with the schedules for those last two. Of course their dialog accounts for that but it bugs some people that they seemingly change in that way. And Leah, well I dunno.
Maybe you could marry Leah and let me know!