(answering this publicly because it got a bit lengthy and because I always enjoy reading how people play their games and maybe other people will be interested as well??)
Since I’ve added ACR to my game, I pretty much let my Sims determine their own fate – which of course will take into account their turn-ons, turn-offs, jealousy settings, gender preferences, etc. However, as you might expect with ACR (especially in a large dorm where only two or three of the Sims are controllable and everyone else just runs on free will), there are bound to be a ton of unplanned hookups. 😛 In that case, I tried to pair off my Sims with who they matched with best, but in some cases my own “ships”, if you will, got in the way. 😛
I liked Sheila and Alfred together from the start – they hit it off fairly quickly, but then out of nowhere he started acting like an ass and they had a bunch of negative interactions and he was constantly engaging in romantic interactions with, like, every other girl in the dorm. I even had Sheila fall in love with the evil warlock NPC instead, and with another dormie Chase (I later found out that ACR randomized his gender preference to male but I had already forced Sheila upon him so now they still have a weird “in love” relationship :3). But somewhere after that, Alfred kept calling her, visiting her, initiating romantic interactions, etc., so I just let that play out. I think they’re only one-bolters, though.
Same with Nate and Tabitha – although you’d never believe they were one-bolters by the way they act. XD There was a time when I moved Tabitha out of the main dorm and Nate fell in love with another dormie (his best friend). I’m a sucker for the best-friends-in-love-who-can’t-be-together scenario, and I was *THISCLOSE* to breaking off his engagement to Tabitha in favor of the other sim. D: But when he next reunited with Tabitha they were just so cute and so in love that I couldn’t bring myself to do it. D:
In my last hood, I had one couple predetermined from their inception in bodyshop – and they were adorable together. 😛 But the rest of the pairings were based on chemistry alone. In fact, one of the couples were paired together on a blind date, hit it off, got married, started a family – and that’s where Tabitha came from. :3 Out of all the kidlets from the previous hood, she was my favorite, so I extracted her and aged her up and moved her to Sycamore Cove to start a life of her own. /tangent
Well, that was a lot more information than you asked for. XD But it’s crazy how a few mods can stir up enough drama in the game to keep it interesting and unpredictable! So the short answer to your question would be – I try to use the chemistry system and let ACR have its way with everyone, but my own bias tends to get in the way sometimes. 😛