Hi, I have been in the window fitting game for nearly 20 yrs and in my opinion the rehau profile is the best as regards ease of fit, appearence and mostly because to date (touch wood) i have not had any form of colour problems.
Most UK fabricators of windows will use the cheapest profile available whilst some will only use "virgin upvc" as supplied by rehau.
I have only had one tramsom section go a greeny tinge a few years back when using a Deceuninck supplier ( only used them for the one job where i had to match profiles!). since then i try to fit rehau wherever possible.
I'm unsure of the exact Deceuninck profile names but I would say it's comparable to rehau and if it's white you'll have no trouble getting beadings and trims to colour match with it as the Deceuninck company makes trims in the exact same colour, unlike some selecta profiles which look grey when next to a nice white Deceuninck or rehau.
one thing to look for with deceuninck profiles is that small narrow sashes are a bugger to glaze as the beads are a bit fiddly if mitre cut, they are much better if the beads are scribed or milled, I once had such a problem that i hit the bead with a rubber mallet and cracked the weld!!
That could also be something to do with the individual supplier.
Hope this has helped, PAUL.
ps rehau really is the dogs*******