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.