I have an older version from wcw and the new gardiners backpack and I did write a review some months back.
Over the years my old wcw backpack has had to have modifications made to it, the battery is prone to movement and the connectors come off, the charging connection is normally the 1st thing to go and I have had to re-gig this.
The switch is normally the next thing to play up, mine is iffy at times.
I have had this backpack for over 3 years and the pump and battery are still in full working order, the body is still in good order apart from the usual wear and tear.
The gardiners backpack is a different animal, at first inspection you can see a better build and quality, but the biggest failure is the carrying handle, when the backpack is full, it seems a lot heaver than the wcw one to transport around, because of this I have mine attached to a trolley.
The flow control switch is something I don't really use, I only use one flow setting and that is full blast, but if I was to use it I think it would be a problem, the unit is located underneath the on/off switch and if the user was wearing large gloves he could find it difficult to locate and adjust, ideally this would be better if it was moved to the top of the backpack.
Overall which is the best backpack, well they both do the job that they are built to do, if you have a lot of houses that require you to go though customers houses and tight spaces, then I would recommend you use the wcw one, if though you are happy to have it strapped to a trolley then the gardiners one is the one.