One of two diffusers to buy...wich one and why?

To be attached to my Speedlite 580:
1.LumiQuest LQ-105 Promax System Kit ,or
2.PRESSlite VerteX
For the moment,I just can't afford to buy both (though I'd like to experiment myself).
I need a diffuser just for the sake of not being "crippled" when I shoot portraits/groups in some "flash non-friendly" conditions (coloured walls,high ceilings,etc,etc).
Both options were choosen because of portability and apparent flexibility of use.
Please share your experience!
Regards,

You cannot go wrong with the Promax System, though it works much better when you use a "bracket" that allows you to keep the flash directly above the lens regardless of the camera's orientation ("landscape" vs "portrait" position). That's the combination that I use.

Thanks SkipD and,if you don't mind,please post a link or two showing the bracket you said you use...or something similar,at least.I'm really struggling with the multitude of photo-related gadgets and just want to know what to look for.Thanks!
Regards,

The Lumiquest Softbox III or Softbox LtP are both very effective when shooting close to the subject.