you'll be very very lucky to find anyone who has had both, so any answer will be subjective and wholly based on the one that they own. I'd therefore say the R4, its great, the P410 could be better, but I've no idea .
If you like quiet (soundproof padding), little dust build up, effective filters, elegant looks, great airflow (not saying the 410 doesn't have that) then do get the R4. One negative thing is that, the case can be quite heavy, but as long as you don't move it around too much, you'll be fine. It might get cramped if you add water cooling in.
Review on Define R4: https://www.youtube.com/watch?v=-FdpIrr3JNc
If you like spacious room, great airflow, speed fan controllers, great cable management, a cool funky case, get the Phantom 410.
A more extensive look on the 410: https://www.youtube.com/watch?v=eREKsgNKYD0
FRONT, 2x120mm or 1 X 140mm (1x120mm included) <--- So here
REAR, 1 X 120mm (included)
SIDE, 1 x 120mm or 1 x 140mm
TOP, 2 X 120/140mm (1 x 140mm included) < ---- or here
Thanks for the answer guys! However, I think I'll still go for the R4 because I want more silence in my build. I'm also leaning onto the Noctua NH-D15 cooler.