giddybiddy is right of course, it's all very subjective and based on your own and your friends' experiences. Others' mileage will vary, for sure.
I was going to suggest Eastbourne too (though only 13+ entry, unless that's changed), or Bedes, which has amazing facilities although not the most academic environment. Or for an all-rounder experience, Battle Abbey or Mayfield both get decent results. Mayfield is all girls of course and is perhaps a bit Goddy, based on what you said upthread. Battle Abbey used to have a bit of an odd atmosphere imo, but my contact isn't recent. Don't forget everywhere has minibuses for day pupils.
I actually think the tallest part of your order is wanting a bright, engaged peer group without the terrible pressure of Brighton College, so here's a left-field suggestion for you, and that's Priory in Lewes, if you are (or, ahem, could be) in the catchment. It will spark some pearl clutching, I expect, but is a really good school, except for the sports facilities, which are a weak spot for obvious reasons. Teaching and pastoral are strong, especially art/music/drama and maths/science, and there's a concentration of interesting, well educated families in Lewes who all choose it in preference to Lewes Old Grammar.
Happy to chat by PM, Baloo. 