I would like to see more villains RO. A RO that would be totally chill with murdering hundreds of people but totally adores and respects the MC and those they consider family. A RO that couldn’t care any less if the whole world burns, as long as those close to them remain safe.
Probably why I like Demonheart so much 
So… probably not for everyone, but I’m a sucker for a doomed romance. If my lover is dying, leaving, forbidden, etc, them I’m hooked, completely.
They gotta leave a strong impression on me. Doesn’t mean I can’t romance other kinds of ROs for my other characters, but for me personally I really like if the RO is someone who is memorable. Confident or charming.
Yeaah, I’m the opposite. 
I’ll take a happy ending, thank you.
at least…if we lack kleenex , we know who stole them lol
Same… happy ending is prefered 
But definition of “Happy” could be differ though…
I like all personalities and will usually try out every RO just to get the most out of a game. But the ROs that impact me the most and leave me thinking about them are the ones that develop into a strong friendship or trust before they become romance. I think in general I prefer the buildup to the romance more than the romance itself, so if that development between characters is well written I love it. Oh and I won’t say no to some angst or jealousy thrown in there for good measure.
In terms of personality though, usually my favorites are super badass or capable characters that become really awkward during a romance. I love that.
In term of personality and traits, the most appealing for me are love interests who are Cryptic, Mystique and Elegant …
Example are Lilith from Curse of the Spirit, Oriana of Heart of the House, Maria Agustina from Tin Star and Lady Katarina from Guns of Infinity
She was super interesting. 
Just wish we got to hang out with her more.
Okay, I change my stance: It’s okay if a big, stronk amazonian woman warrior sweeps me off my feet. Literally. The only exception!
Same.
Well I’m late to this covo, but if anything, I’m not picky on my RO so long as they’re developed and written well, I’m fine with any archetype. I think it’s cuz I’m usually focused mainly on the actual plot (unless its a romance focused novel). So yeah personality wise anything is fine, however I do slightly prefer guys that aren’t assholes over guys that are, even if they had a really tragic backstory as to why they act that way, like nahhh man. I have more of a soft spot for the dashing/sexy/suave characters, heck I even have a soft spot for brooding/bad ass/stoic RO’s but ones that are downright dicks? 
Haha, then Jun/Junko from Samurai of Hyuga is the RO for you!
Agree… Oriana is the ultimate antagonist (or perhaps Protagonist in different perspective ) who is willing to sacrifice few in order to save the world , and most interesting was that she is still learning humanity in our world in addition of extreme loyalty to the core 
By contrast , Sophia is selfishly cunning (for my opinion ) … disguise herself in a perception of an innocent Damsel , as Oriana stated always Sophia could had void the contract and set Oriana free if she think all Oriana’s doing is evil, but Sophia didn’t simply because she knew very well the portal will breach and the world is doom once Oriana is gone … but at the same time Sophia never intend to bear any responsibility except blaming others… Sophia even ran away during the night of trouble and assuming Oriana will fix it by herself
Honestly , Sophia looks like one of those manager who like to play office politic , just know how to maintain deceptive face value in front of others but playing the blame game behind the scene :-)
Hence I have no regret taking the power from Sophia and set Oriana free … i would rather enlist Oriana’s aid based own true loyalty than bind her with a chain , good thing is Sophia finally see the light at the end of story and reconcile with Oriana
I have found that I really enjoy one or two very detailed and specific romance possibilities, assuming of course, that one of them suits my tastes
I’m one of those indecisive people that if I have too many options to pick from then I find I can’t pick at all or I’ll end up picking the very first vaguely suitable RO and then have weird pangs of regret for the whole game… X’D
For instance, I haven’t played ZE: Safe Haven yet, but I think I read there are lots of ROs (???) And in my head I’m like… Nope, not afraid of da zombs… Afraid of being unable to decide on an RO 
I don’t have a specific personality type that I look for. I prefer to see who ‘matches’ my MC’s personality. The setting can also affect that. I’ll take an alphabro who’ll protect me in a violent setting, but I wouldn’t be as likely to like him in an office setting.
The most important thing, as with most aspects of interactive experiences, is that I want my choices to matter with the RO. I want to ‘earn’ them a bit, but not so complicated that I need a guide. They should have personalities and expectations that I can choose to accommodate or not. If I’m with them, I want it to matter in the conclusion, not just a “and [RO] is by your side.” laziness.
THIS.
Well If you mean in what type I like in romance option’s I would say it varies on the plot and tone of the story and also if you have to play a certain way to get that character but in general for personality…
In terms of full-fledged personality, I usually go for romance options that have a hard time accepting that they have feelings for the main character(not aromantic) but are all for, no rejections, with being in a sexual relationship with the main character or something similar to that, I never have seen this be done in a choice game before but I have seen this type of personality in other ‘games’. If that’s not available I usually go for the best friend type whether they are the main character’s best friend or they just seem like it and if that’s also not available as well then I go for the boy (or girl) next door type.
But in general, I like characters who aren’t just there for extra scenes no matter the personality or appearance of the romance option. Although in some cases if I find a romance option(s) who I feel is kind of problematic, and I don’t feel that’s the author intent I ask the author about the romance option(s)
Like a friend with benefits that catches feelings?
I tend to pair MC with ROs who I feel need it the most. More often than not it’s the unhappy one of the bunch.
Is there a RO who has unrequited feelings for MC and is clearly miserable? I’ll pair up those two real fast. Is someone suffering from troubled past? MC is coming straight after them.
I haven’t played many CoG games yet but my absolute favourite RO at the moment is Patch from Fatehaven. Their backstory hit me real hard.
tl;dr
I prefer characters with problems. They stirr emotions inside you.