One part of this not really covered is specifically how many time zones are you out from your home and when are your arrival and departure times in relation to your home timezone. In my opinion, these are the critical questions as to whether you can get adequate rest in 24, 36, 48 or 60 hours. As many of these flights are single daily flights, the layovers that are not multiples of 24 hours are usually not practical from a commercial standpoint.
I did a DXB-IAH trip with a 48 hour layover. The time zone change was 11 hours difference. On our first day there, I absolutely hit the wall at the time I would have been reporting had the rest been 24 hours. Our airline then made the layover 24 hours and was inundated with fatigue reports.
I then did a DXB-GRU flight where the time zone change was 7 hours. The shorter (26 hours) layover was quite do-able because my body wanted to go to bed about 8-9 hours before report time.
What's alarming are the number of replies that indicate being rested is not even a consideration, but rather maximizing days off at home or minimizing the layover in a less than desirable city. I don't do as much ULR flying as many of my colleagues but the rest issue is incredibly important to safety. That we have so many pilots willing to blow off the safety aspect is damaging to our credibility as professionals. As always, we seem to be our own worst enemy.