Did 4 sectors on QR recently, two on 787, 1 777 & 1 A380.
The 787 is definitely tighter and the entertainment box is definitely a problem if you have long thighs & big feet like I do. On my DOH-CPT I sat with 2 other adult males and we were rather tightly packed in. The AC also failed so we boiled. On the JNB-DOH leg I got lucky being seated next to a rather pretty girl & having the middle seat between us empty. Sadly she was on the way to see her boyfriend. If you're over 5'9 I think the 787 would be problematic for LH & sleep.
The 777 was decent especially if you get the last row in the first section of economy which is 2 seats making it easier to get out.
On the A380 I have always found it best for sleep to have the window as I cannot sleep sitting up. I put a few pillows against the wall and crash. It's the best sleep I've had on a commercial flight. Got extra lucky as the DOH-LHR leg was <50% full in economy so we spread out to have our own aisles. I just feel bad for the people around me that had to endure my snoring after being awake for 36 hours.