While I think the instant gratification of immediate XP awards AND the ability to anticipate exactly how close their characters are to levelling up makes XP the preferable system for the vast majority of players, the truth is that as DM I'm already working WAY harder than anybody else at the table and I just flat out can't be bothered with XP.
In most campaigns, I do leveling like this:
- Character reaches level 2 after 4 hours of play
- Character reaches level 3 after an additional 8 hours of play
- Character gains an additional level roughly every 16 hours of play thereafter
My sessions tend to be 2,3, or 4 hours in length.
In some adventures, I find it more appropriate to award levels based on storyline achievements, so I do it that way.
I think the only time I've used XP in 5E was the first time I ran Lost Mine of Phandelver, and the first time I ran an AL season. In both cases, I did it because the adventure did most of the work for me in indicating how and when to award XP.