I had the predecessor to the defy (the OCR) before I got my TCR. For me, the TCR is better because I have fairly long arms and like to ride with a significant drop from my saddle to the handlebars.
If I were you, I would ride them both and if you feel comfy on the TCR, get it.
As to the disc brakes, they would be good if you were riding in the winter but otherwise they are just heavier and more complicated than rim brakes. I would also note that they are old tech (cable actuated) so they likely won't be considered a desirable feature in the future.