Of their NTR sims, I'd say Leanne is the best (haven't played Monica so no opinion on that); it has the greatest variety of scenarios, story lines and endings. Misaki is the only other one I'd fully unlocked everything on.
Out of all Acerola games I've played though, I definitely enjoyed (and played) Treasure Hunter Claire the most. The crafting system in Colette was more of a hindrance than anything (plus the small boobs option didn't really fit), and Tear was just kind of lacking.
Phantom Thief Celianna was garbage.
I've gotta say I've liked a few Acerola games, but they were all the cum collecting battle variety I guess.
First one I ever played was Claire, which then led me to seek out others by the same author. Next on the list would be Colette, which was amusing as well.
I tried Tear, but meh ... kinda quit after a few hours, still haven't gone back. The whole failing on purpose, just to get scenes from the sister annoyed the heck outta me since I don't want to fail 'the mission' on purpose, which was basically just 'don't do a damn thing, just go to sleep w/o doing anything'.
In the end, I didn't get a single sister scene yet and just got kind of bored with it. Maybe I'll get back into it to finish someday.
Tried Celianna, but couldn't be bothered to keep playing past the first hour or something. The gameplay just didn't agree with me. Absolutely not my kinda thing.
The other line of games, guess I only went through Liana. It was playable, but it's not the type of game I go actively looking for.