Scarlett, Scarlett and... Scarlett! I love this character so much, she more or less became best girl within 10 chapters for me. I really liked the idea of her trading sexual favors for "protection" of her friends, but it looks like the main branch is moving a bit away from that. Maybe it'll be revisited in the future. As I've commented in previous chapters, A Scarlett/Heather threesome is an absolute must.
To give an actual answer, I also find CR Lisa is also infinitely better than her AR counterpart. Not having the narrative shackles of a preexisting relationship with the MC lets her be much more playful and adventurous, without railroading in the inevitable melodrama. To borrow from one of JohnLocke's ATC threads, I like the idea of Lisa having a bit of a dom streak which catches her partners by surprise (as a but of a spoiler, I'm hoping to capture that energy in my own thread).
I'm also really liking Grace, but I'm torn between wanting to see her and Logan as the OTP vs seeing her seduced by Lance.
Scarlett is a character that I quickly grew to love writing as well. Her ability to stand up to others in defense of Logan and Terry (sometimes even using sex) was a trait that I easily see now that it was a bullseye on my part. You're right that it makes her an explosive partner for Heather in a threesome. I'm yet to explore what happens when she gets horny enough, I hope everyone enjoys my next chapter when I do that, lol.
Lisa without shackles indeed is a fun character. I only gave her that failed relationship with Clark as a nod to the old version, but she was way more assertive here. I remember writing that she dumped him by kicking him in the nuts, lol. I also think that the group of friends I created around Grace, which includes Lisa, was a good decision, as they play well with each other. Lisa's fiery personality translating to a dom streak in bed tracks with how I see her as well.
I won't comment much on Grace regarding her main pairing because I want to avoid bigger spoilers, lol.
I've been playing around with the idea that Logan could use a new male foil/antagonist.
As I see it, the two "main" villains from the original canon were Kurt and eventually Brandon.
Kurt was obviously designed to be the kind of brash, cocksure womanizer who was really an opposite the more timid, generic self-insert that was Zack. Originally, it was pretty clear that the main purpose of ATC was to tell different stories of Zack as a proxy for You The Reader getting the girls, and Kurt was more or less there for you to stop. Over time, more layers were added to Kurt to make him more likable (JoeSte91's epic turned him into the hero), or at least less disdained.
Brandon's villainy was more of an evolution. The earliest threads place him as an old friend of Zack's, who would encourage and help him/you on his/your quest. As more stories were written and there needed to be a reason to "free" Ashley up as an option, he was gradually flanderized to be a meat-head jock and bully who absolved the readers of the sin of hooking up with the girl in a relationship. Ashley's evolution into a childhood friend of Zack's effectively forced her relationship with Brandon to be eternally doomed.
As to why neither of these character's really work as a proper antagonist to Logan:
The original girls' characterizations were quite simple, with many of their personalities evolving over time. I think the biggest of these was Heather, who is (for the better) a much more headstrong and confident character. It's because of this that's it's harder to justify Kurt as being an unrepentant asshole to Logan because:
1, Logan isn't that generic, self-insert cliche who only reacts to what goes on around him. I can easily see Logan actively standing up for himself if he is personally antagonized (he still has his own hang-ups when it comes to others around him though).
1, Logan is a more confident character with a MUCH stronger/better friend and support network. In retrospect, Chloe and Gavin were quite weak willed. That's not an inherently bad thing, but enabled the three of them to be collectively steamrolled at times.
3, A modern Heather would instantly tell him off, or even have him around in the first place. I can't imagine the combative, confident heiress being kowtowing to her estranged mother's sister to put up with an irredeemable Kurt, especially one that she knows will be especially creepy around her friends. Either he would have to have multiple redeeming qualities (which weakens him as an antagonist in this kind of story) or she has no knowledge of his personality at all, and is meeting him for the first time (which is a whole new character at this point).
Ashley has less of a relationship with Logan, and has a much stronger relationship with her friends who are also collectively smarter. If Brandon is to turn into the dumb meat-head villain as in previous iterations, I can't exactly see him being a threat to the other girls. Each one of them would tell him to hit the bricks, except maybe Sharon?
In my view, talking about the younger cast (teens and college-aged characters), the biggest villains would be Dylan and Shawn. Shawn comes from At the Cabin's early days, where he was more prominent, but then ended up getting less used with time. He's a guy that used to be Peter's friend and then developed a penchant to seduce girls at a level that those girls became his slaves, he gets off on control. Dylan was a character that I created to be a rival for Logan in a story that's no longer up on the site, but that was the version of Logan who was rich and lived in AR his entire life. Now, for Copper Rocks, I've been building Dylan in my mind again to use in the future arcs, but he basically has a similar mindset of Shawn, he wants to be a puppeteer controlling the girls, disregarding their feelings. In the previous version, Dylan even got his inspiration on Shawn, but now I'm still deciding if that will be the case.
Kurt and Brandon are more like situational villains, where they'd be rivals to the main character for a specific girl, but not evil like Shawn and Dylan. I'm already trying to make Kurt more likable and just someone who does wrong by accident in his pursue of more fun. Brandon, I can only see him becoming a villain if Logan gets interested in either Ashley or Madison, but because he wants to block anyone from them, not because he hates Logan.
Reactive, that's the word I'd use for Zack. He'd only stay back and react to the stuff that happened to him, almost never pursuing his plots actively. The facts that Chloe and Gavin were even more reactive than he is and neither of them really helped each other to evolve from that eventually made things quite dull for me. I know not everyone would agree with me on this, but that's how I feel. I know that there are still people who roll their eyes to the idea of Logan, Scarlett, and Terry, but the truth is, they're more enjoyable to write, to create stories and plots for, and a much more dynamic trio. Scarlett's willingness to help Logan and Terry to do better and protect them from stuff, Terry seeking only Logan and Scarlett's presence in his little world when he doesn't want anyone else, Logan making the two of them pillars in his life and having a difficult time when they're not around. They'll all have to evolve both by themselves and together, but that makes them a better set of characters to work with, at least to me. I've been criticized a lot back when I created Logan, people kept telling me that he wasn't as deep as Zack. While this was true at the time, I think that with this version, I managed to overcome that barrier and those days are finally behind me.
That's why I support Gray Gremlin's Honey Hollow so much. He tackled an idea that wasn't working for me and is doing something better with it. While he didn't change much those hang-ups I had with the older trio, I find it way easier to cheer for Sean than Zack. That's not to say that Chloe and Gavin are removed from my universe, they will be featured quite a lot when I get to tell Paris' story in my thread.