The Jag AWD transfer box is a weak point, but then again the Haldex AWD system in the Audi is ******** too (and permanent FWD until it clutches in a small proportion of the torque to the rear). At least the Jag one is better when it's not broken. The Audi one is prone to breaking too and when it's working the results are iffy.
Depends what you like in a car. The TT, to me, just drives like a stiff Golf. It's more claustrophobic than the Cerbera but with none of the excitement.
The X-Type isn't sporty or particularly fun to drive - but I've yet to drive an AWD car which I thought was engaging or exciting so if you're looking for that neither the X-Type or Audi will deliver. They both feel solid enough and well planted (that's why they're both dull to drive).
FWIW I've driven S3s pretty hard and they're mechanically pretty much identical to the Audi - just as naff and prone to wild understeer on damp corners. The Haldex just isn't very good. The A4 Quattros use proper centre diffs like the X-Type but have pretty poor suspension. X-Types don't drive well on old rear suspension. They use Mondeo estate multi-links and the upper links in particular are especially prone to premature wear on X-Types, with almost ridiculous effects on the drive. On the flip side, for hardly any money and virtually no time, you can make a poor driving X-Type drive like a new one with a couple of new rear upper links.