Personally I'd not buy any of them

but If I had 270 pound gift card, and needed a new drill...
Of the two, I'd go w/ the third, the 18v, it puts out more power (~33% more than the 14v) (, and has more torque (20% more than the 12v and 10% more than the 14v) which really DOES matter when you're putting in lags... plus it's like what 6 pounds more?
Plus, the 18v is pretty much the modern 'standard' for cordless power tools... when the replacement Li-Ions come along, they'll make them to fit an 18V unit but not necessarily a 14 or 12... Dewalt's kind of funny about that stuff...
In a way you're lucky you're in the EU, we still have to deal with all our cheapy stuff being Ni-cad powered... Yours has to be NiMH or better...