It all depends on your cars mods, and preferance. Singles tend to take longer to spool(make boost) than the twin kits if not properly sized. All of the companies above come highly recommended. I'd go to http://www.turbomustangs.com/smf/ and read their FAQ's and search the forum for information that might help you in your search.
I have a 1997 cobra, im lookin to do a turbo kit, im not sure whether to go single turbo or twin turbo, im new to the mustang world, just picked up my car 2 weeks ago. Is there any kits you guys can recommend for me, thanks