juwel hands down on quality, they have one of the most affective ways of building tanks using 5 people!
I'd say Fluval hands down,
In terms of Quality of the tank and stand there is very little difference, [edit: would have to agree though that the fluval doors are iffy]
However when referring to the lights, heater and filtration, IME there is only one winner
My last tank was a Juwel and the one before that was a Fluval, I had both tanks for the same amount of time give or take about 1 month
On the Juwel, the light unit had to be replaced twice, the heater failed after about 5 months and the filter was very quickly ripped out after the powerhead went.
With the Fluval however nothing failed, The heater and filter even went into the Juwel tank after the juwel items failed