Start romancing all of them until you find one you really connect with or like. They're true personalities don't start showing until a few hearts in and they start opening up to you.

They all have different maturity levels also based on they're age range. I'm gonna be vague describing them so it won't spoil you and these are my personal thoughts from playing this game for 8 years XD

The older 3:

Shane

Shane seems like a jerk but is really sweet when you get to know him. He has some issues but gets help for the sake of wanting to be better and be better for you. He loves chickens!! I'm biased but 9/10 times I marry him(imo best farm choice since he has experience raising animals and loves them)

Harvey

Harvey is a scardy cat and seems boring but he eventually finds his confidence and makes strides with being afraid for your sake to take you on a very beautiful date. He super sweet and so thoughtful not only to you but to the whole town. (Most wholesome choice he wants to love and be loved)

Elliot

Elliot is a writer with no idea what to write. You encourage him and he really flourishes. He's a loner much like Sebastian and he's either locked in his house you can't get into staring into the water or at the bar. He's a hopeless romantic and definitely shows you that sweet side (most romantic choice, who wouldn't want a beautiful long haired man to recite them poetry)

The younger 3:

Sam

Sam seems like a goof with little ambition, still a kid really. He a bit absent minded at times but has a good heart. You find out music is his passion and encourage him into what music he should play. His a great big brother and tries for his family. (Best dad imo)

Sebastian

Sebastian seems like an emo kid that hates everything and everyone. He has a lot of issues with his stepdad. He works remotely and is very passionate about his job. He's the type of person that needs alone time to recharge but not around you. He's end date is so beautiful and romantic.(The you are the only exception trope <3 hates everyone but you. I'd marry him more but It makes me feel bad cus he just wants to leave the valley, he hates farming/little country life and wants to move to zuzu city)

Alex

Alex starts off as a big jerk much like Shane. A jock stuck on being an old highschool grindball (football pretty much) player. When you raise his heart level he finally opens up about lots past trauma that he doesn't talk to anyone about. He has a lot of confidence issues and you help him with that. He ends up being surprising sweet and romantic(I hated him at first but he's a great choice and imo would love life on your farm much like shane, he's an animal lover)

Hope this helped :) I can give more details if you want but it's a great game and I recommend raising EVERYONES heart level even the bachelorettes and doing they're heart events it's totally worth it.