Zaino is the best clay i've used but it's expensive. Other than that you simply can't beat Bilt Hamber auto Clay. I buy the soft one you shouldn't need any stronger. Brilliant stuff. Massive pack for £10.
BH stuff can be used with some shampoo and water in a bottle. I like VP Citrus Bling, very versatile product and a great clay lube.
Demon Shine from Asda diluted is a brilliant alternative, very slick. 75% or 50% DS and the rest Water. Very cheap.
Perfect for me is Zaino and Citrus Bling but everyone has their favourites. Just don't buy cheap polyclay mate it's s**t.
don't use poly clays, they're aweful!
one of my favourites is the megs one you can buy in Halfords. born slippy concentrate is decent once diluted down correctly, and it's nice that you can just wipe it off after without the need to fully wash again.
always keep a tub of hot water with some clay sitting in it and swap over after a couple of panels in this weather as it keeps it a lot softer and easier to use.