Guildhests are basically useless and only good for EXP from achievements for first-time completion. If you don't want to spend that much time and just want to get as much EXP in the shortest amount of time, both Leveling and Trials provide the most efficient EXP gains, followed by Alliance Raids and Trials, Normal Raids, and 50/60/70 Dungeons. Tl dr: If you have all the time in the world, don't care about roulettes stretching on for large amounts of time, and just want to maximize your maximum EXP gain, Main Story roulettes most frequently provides the most amount of EXP, followed by Leveling, Alliance Raids, 50/60/70 Dungeons, Trials, and Normal Raids. I will explain my methodology shortly, but for those who aren't interested in the nuts and bolts:

Time for cutscenes were not taken into consideration with the exception of Main Story roulettes, which are unskippable. but just that everyone seemed to know what they're doing, the party didn't get wiped, and the duty was accomplished in a reasonable amount of time. This does not mean that the run was 'optimized' - everyone had best gear, tank aggro'd everything, no one got knocked out, etc. Repeated runs of roulettes were not counted. In other words, I am only tallying duties in which a roulette bonus was awarded. Only the first roulette daily was counted.

Therefore, as of July 7, 2021, level 80 duties were not included because they do not result in EXP gain. My joining a roulette already in progress was not included in this analysis. I ran more than 120 roulettes in an effort to determine EXP gain and its efficiency, because I wanted to pretend to be smart.

Sorty roulette