I like all of them for different reasons! As far as visual appeal goes, I think I like Meadowlands and Hilltop best. I also like the Beach farm, but as far as gameplay goes I tend to prefer the Forest and Riverland farms.
Forest farm because: I like the easy access to forage and hardwood, and also all the leaves and greenery just make it really pretty :)
Riverland farm because: I don't like watering crops, so being able to plant a ton of rice in spring without having to worry about watering cans or sprinklers is nice. I also like fishing a lot, so being able to fish right outside my door is another thing I like about it. Once I get later in game, I also think it might be fun to have different islands for different things, but I haven't gotten there yet.