id say 2.0 evry time tbh. whether in valver or if you go for full fun package n go for the willy
in terms of speed, diff class tbh. loads more torque throughout the rev range with the williams, doesnt rev as high as std as the 1800, but then you dont really need it to, if its std, and the limiter can always be moved up the range with a cheap chip.
williams has wider track, heavier duty roll bars, torsion bars etc, so does handle that bit better as std. add coilies etc and the margin just keeps growing. if u see a valver thats had the wide track etc already fitted....then go for it, as you would probs want to upgrade to this in the future.
as above, williams is quite a bit more to insure. but so much more fun out the box, and quicker to boot
choice is all yours really, with these cars its swings and roundabouts, a clean valver with 2.0 lump and widetrack will cost about the same to buy as a decent williams. so in that respect theres not much in it. but..........the williams will hold its value for far longer than the valver.
personally id go for the williams every time, i dont like getting rained on from the shite sunroofs, i dont like my roof buckling after a heavy session thru the corners. thats also why id never ever have a willy 3. u might as well just get a hybrid valver as a willy 3 tbh.