My two cents on the various eligible candidates...
Abigail is in love with the idea of adventure, but she's not really that cut out for it (see also: 10 heart scene). She acts like a rebellious teen even though she's listed as being in her 20's. She's probably one of the least mature candidates on the list. But hey, at least she won't be ruining any plans by falling hard for you, since she didn't really have any past 'get out of dad's house'. Which, I suppose, makes her the quintessential 'Waifu', but not particularly interesting if one wishes more depth than a puddle.
Maru is... well, let's be honest here. She's Ace. Which is great for her, but means she's not really a romantic candidate, at least for me. Even all the way up to her ten heart event, where most of the candidates get anywhere from flirty to... ahem... (Penny's 10 heart scene...), Maru is more interested in a lab partner for a platonic life partner, and that's not really what I'm looking for in a marriage.
Emily is easy on the eyes, and has a fun and bubbly personality. But rule number one: Don't date crazy, and she's taken her 'granola hippie' shtick a few paces too far. There's times I'm not sure which version of reality she's operating in, which is a bit disconcerting. Plus, were I to seriously date her, I'd have to... have a respectful discussion with Clint about creeping on my gal, and that would likely end up with the town no longer having a Blacksmith, which would be a shame. I mean, don't get me wrong, she can be a fun bag of crazy, if you wanna get your freak on I don't blame ya. But between not knowing when she's gonna get some odd idea in her head and Clint perving on her nonstop... yea, more trouble than it is worth, in my opinion.
Penny, at first glance, seems to be an excellent romantic candidate. She's the schoolmarm, so she's fairly intelligent. She's not afraid of a hard day's work. She's good with kids. She'd make a very good farmer's wife, someone intelligent enough to be an equal partner in the business. Except... she's got some baggage. First, there's her mother, the town 'drunk redneck' stereotype. Who would then be your mother-in-law. Yikes! Then there's the fact that she seems to be more looking for an escape from her current life than looking for the next step in her life. She's offering what she thinks you want because she's afraid of rejection, and that generally ends up with a bunch of drama on down the line. So, as long as you can convince her to communicate about her actual needs and desires, it could work out. But she seems the type to hide her hurts and offer what she thinks you want even if it isn't what she wants, and that's not healthy for either of you.
Leah is the fifth and final female candidate. She's not hard to find, she can be found several evenings a week at the pub, enjoying a salad and some socialization (instead of holding up the bar like Pam or Shane). She's got baggage, but she's also handled it and taken care of it. She's moved on. She's an independent hard-working lady who is familiar with nature and the bounty it can offer. She's got an ex, but unlike Emily who seems unwilling to tell Clint to his face to cut it out, she's sending a clear and unambiguous signal that her ex is the one who won't let it go, while she's moved on. She's also a talented artist, working in several mediums, and how you help her with this is equally important. You neither take it over for her nor hand it to her on a silver platter. You support her, but she's the one doing the work for herself. She's a strong and independent woman who needs no rescuing, and chooses you not because she's trying to escape something, but because she wants you for who you are. That's a good foundation for a relationship.
Then there's the guys...
Sam is... well, he's basically the male equivelant of Abigail: a twenty-something acting like a spoiled teenager. He's got the skater boi vibe that highlights his immaturity, his life goal is to be in a rock band... he's got no plans for his future that are remotely realistic. He at least does show some work ethic, working a minimum wage job at Joja, so he does have that going for him, and he's a good 'big brother', so presumably would make for a decent father. But the boy has some growing up to do before I'd consider him seriously as a romantic partner.
Elliot is the quintessential 'starving poet'. Dashing, debonair, honey'd tongue... and almost no substance. All the world is merely a play to him, with himself as the star of the show. He's someone to date, to have fun with, but for a deeper and more meaningful relationship? My biggest romantic rival would be his hair. Pass.
Shane is not in a healthy mindset at any stage in the game. He starts off as an alcoholic, who drinks to forget and to escape his problems, and who is intent on drinking himself into an early grave. This is kind of a huge red flag. Even after the gut-punch of his niece's reaction to seeing him in a drunken state, he doesn't really clean himself up that much. He puts on a facade, but he still goes drinking every night, he still tries to escape whatever he was escaping from, and won't let anyone in, not even a spouse, and won't share what caused the pain in the first place. That's another big red flag. He needs AlAnon and therapy, not a romantic relationship, and needs it in a hurry before he goes from passive to active suicidal ideation.
Sebastian, at first glance, comes off as the 'bad boy'. He's a smoker, rides a hog, leather jacket... that whole thing. But there's a lot more to him than meets the eye. He's one of three candidates who actually has a career (Shane and Sam's dead jobs at Joja don't count). He's had issues with his stepdad not really understanding him, which has caused family drama. Which is why he affects the bad boy look. But deep down inside? He's not a bad guy. If I have any reservations about dating him, it'd be that it would feel too much like trying to date myself.
Harvey is the only one of the candidates with an actual stable career in a respectable field. He's also the oldest of the bunch. He's kind of a stick in the mud, but some people like bringing the turtle out of their shell, and this is a prime opportunity to do it. His fascination with aviation is endearing because he doesn't have a false hope of doing it himself, and isn't planning on giving up his career for it. So he has his priorities straight. For someone who wants evening snuggles and a solid, dependable spouse... you'd have to go a long way to find a better one.