Going: YYZ to LAX 5.25HRS, 3HRS layover, LAX to MEL 15.25HRS.
Return: SYD to LAX HRS 14HRS, 5HRS layover, LAX to YYZ 5HRS.
United Airlines, Economy for the whole trip except SYD to LAX I was upgraded to Premium Economy and had an empty row entirely to myself.
I can easily fall asleep on the plane so I usually take the window seat and sleep/listen to music the entire time. Rarely do I get up to even use the washroom unless it's a really long flight. Window seat also gets a little extra room to lean and leg space so its not too bad.
TLDR: PE not worth the upgrade price, unless you can get it for free