If you are sure you want diesel then your options are
1.9tdi PD - oldest engine maps to 140ish. Only a 5 speed box.
1.6tdi CR - not a performance option really but maps to 140ish. Had a dpf.
2.0tdi PD 140 - these are the older engines and maps to about 180ish
2.0tdi PD 170 - not many maps available for this one due to various issues, but can map to 200+. Has a dpf.
2.0tdi CR 140 - newer smoother more linear and has a dpf. maps to 180ish
2.0 Tdi CR 170 - these best and most expensive diesel option, Unit 9 will tell you more about mapping this but well over 200hp even with dpf.
CR means common rail, introduced sometime in 2009 with the facelift. PD means pump duse injection, pre facelift only so cheaper.
The highest spec diesel is the FR or Supercopa FR. There is no Cupra diesel model this generation. 10k will probably find a half decent FR CR 170. Example
http://www.autotrader.co.uk/classified/advert/201508276398687
If you want performance and tuning options above all, have a look at Cupra 2.0TFSI models. Remaps to 300+.