I would like to know this since i went and bought IHost billing script what script would u say was the best billing script?

Well there are really a ton of them out there, i am a whois.cart junky, but modernbill and clientexec are two others i've used and am quite fond of.

hmmmmm Well its a bit late asking once you've bought it?

The only billing system I've worked with is paypal though, so I can't really off you a proper answer.