There's a lot of posts about who the best girl is. I think it's too soon to call for me. They all have a lot of appeal. The two in the lead, for me, are Serra - because I too adore the sexy pervy roleplayer thing, and Gracie - because her sheer excitement levels, unabashed positivity, and my partiality to the colour green. I also really enjoy both of their bodies, which some might find odd since they're on opposite ends of the spectrum. Variety is the spice of life, though!
I really like all the girls a ton, too. I'm not the biggest Tsundere fan, but with Celeste it's easy to tell she's just embarrassed or not willing to face her true feelings, and I like that about this particular Tsundere. The laid back attitude of Lillian is relaxing, and I could see the MC going to her when he needs a sense of calm. Alex is very obviously incredibly loving. All of them are super cute and sexy.
I almost wish it'd taken me a while to find this game, because I'm kind of disappointed I can't visit any of the other locations yet. The secondary characters seem really amazing too. I'm looking forward to meeting them.
I think if the game doesn't end up with a true harem ending, with how amazing all these girls are, I might lament having to choose for eternity.