I cross over my mains into my sub at 80Hz. I tried everything from 50Hz to 100Hz, and found that 80Hz resulted in the smoothest integration. However, I cannot say that 80Hz would necessarily work best for you, since, after setting up several mains/sub systems in several rooms, I came to the conclusion that the choice of crossover frequency is very system/room dependent.
Another thing to keep in mind is that the perception of of the "best" crossover frequency will be influenced by other parameters of subwoofer setup, such as placement, phase, level, and time alignment. All of those parameters interact psychoacoustically, so it is often challenging to identify which parameter needs to be adjusted. In my case, it was a frustrating process that took several full days of experimentation distributed over a couple months.
Having offered those words of discouragement, I will say that it is totally worth it, so hang in there!