Like with your stereo on max volume, full performance is something rarely used in a car. As an ex-owner of both cars, my main addition to the debate is that the Willy was IMO the superior "pootling" car: the damping and comfort were great despite the bespoke harsh suspension rates and 85% of peak torque at 2500rpm made brisk driving a real pleasure at low speeds.
I honestly believe that the Willy and 16V are the greatest hot hatch pairing yet, better I might I add than the excellent 1.9 and 1.6 205 GTis Ive recently had the pleasure of driving (mainly IMO due to the stability, suppleness and poise... no sting in the tail and all that). These are still THE cars of my driving life and deservedly the darlings of the misty-eyed motoring press.
The 172/182 have too much talented competition and dont move the game on enough IMO to take the mantle, although time will tell. The issue would be resolved IMO by making a limited edition 182 with a garish colour-scheme, 2.2 bottom end and cult-inducing name.
Watch out for me in my "ID" option coloured 182 soon though, for thats where Im probably headed next!! Lets just say that my Cliosport membership will be getting renewed.
At over a decade old (more so for the 16V), time plays a bigger role in the performance difference between the two. That said, my old Willy made way over 150bhp... just like most F7R 2.0 engined cars. The main difference was noticeable up big hills and the flexibility, but you really have to be discerning to notice most of the difference otherwise (and yes... I am discerning).
So, there we have it. Three cheers for the Valver and Williams... and a tear from my eye, of which they are both still the apple.