I don't believe you will hear any sound quality differences between the C.A.B. and the WOSIII plugin. It really depends on HOW you are using them.
With the C.A.B. you can play live in real-time going straight into your DAW using the C.A.B. if you know what preset or settings are going to work for you. Using this method, you will not be able to change/edit the cab emulations later. This is fine if you have gone through and tweaked your sound as a 'keeper' tone.
With WOSIII you need to capture your amp sound direct with a load box (or DI from your amp sim), then add the plugin to your guitar track and tweak to your satisfaction. Either method will yield same quality results. It just depends on your workflow. It should be noted however, that if you buy the C.A.B. you also get WOSIII with all the same cab options included.