I own a few TU engined cars aswell as the 2.
Id say for track days id get a saxo, they are alot easyer to work on and upgrade parts for, easyer to get parts for as theres so many that have been bent, and different models parts generally tend to fit easily.
Chassis wise they are great out of the box imo, but can be upgraded easily, depending on budget id get a mk1 (even though mk2 looks better) can get a vtr (8v) if you are worried about money, put decent brakes on it and suspension and it will be quick on track, proven when i hammered a few big spec saxos and a 172 on a track day lol.
Vts is the engine to have but insurance???
Gtis tend to hold value more as pug owners think they are worth more than citroens for some reason, even though its the same car bar the leathers in the late spec gti.
any questions drop me a pm, or get on
www.sax-p.co.uk I moderate the forum there and theres plenty of people willing to help out if you have questions about them.
Ry