IF you were to chuck loads of money at it then the 2.0 hdi would be better...all the way...
you can get crazy power out of them if you get it done right....
with an intercooler on the 2.0 hdi you;d be looking at over 150 bhp and more than 260 lbft torque....don't forget that the 1.6 is a 16v and the 2.0 is an 8v so bhp gains will be similar to a point but the torque will be more on the 2.0 because it is a big capacity....
I'd got for the 2.0...there are more tuning options for them....