Both are reliable, but the N47T is the one to buy if you envisage a 20d.
1. Power difference of 15kw and 40nm.
2. Issues leading to timing chain and turbo failures sorted with the N47, more over the with the N47T (Apr 2010 and onwards)
3. Preventive maintenance would be regular oil changes, egr-delete, swirl flap-blank and a decat on both platforms.