What are the best WAF vendors and models out there?

The best one presently in market ( as per my experience) F5's BIG-IP ASM

others:

Imperva's SecureSphere, Barracuda's WAF, the Citrix NetScaler MPX WAF and Dell's Sonicwall WAF. Qualys' WAF and Imperva's Incapsula are WAF products covered in the cloud/hybrid category, while the ModSecurity Web Application Firewall is the lone entry addressed in the rather unique code integrated product category.