For a lot of sims I consider the cooking, fishing, gardening trio of skills a requirement for at least one YA in the family (if im not playing Bridgeport where I always make a single sim) because they help so much. When I see this "utility sim" is going to die soon, I have another sim take up the traits and skills for cooking/fishing/gardening. So because of that my most used boarding school is the School of Peace and Love.
I really like that one because even if my sim is going to skill in other things they will always get the "utility" skills that will really help them with everyday life. Plus, it's the cheapest school at 800 simoleons.
Of course as Ricalynn said it really depends on what you want your sim to do... so an ambitions-type sim would probably go for the LeFromage Art School, a more rabbithole sim might go for the prep school... etc
Something odd I realized while reading Carl's guide on the boarding schools is that the Sports Academy and Military school teach Cooking and Gardening/Handiness respectively. I'm not too surprised about handiness because I think it's one of the requirements for Military track but it's nice to b able to learn the "essential" skills from boarding schools focused on other skills.