Right-to-left 1h swing glances way too much, even with perfect range/position. Left-to-right and overhead don't seem to suffer from this malady.
1h thrust, on the other hand, is just totally unpredictable. If you actually aim it at the guy, it will glance. So you have to aim it in some random direction then spin into your target. People rage at this maneuver, but it's only done because it's the only way to not glance with the 1h thrust. On top of this, there is no rhyme or reason to the 1h thrust hitbox calculation; sometime I can thrust directly into some AFK guy's skull and it misses, then another time I'll thrust and headshot some guy like 6ft off to my right.
2h is so popular because the animations are reliable; they don't glance unless you really screw up, and the hitboxes are logical. Every 1h thrust/right swing attempt is a potentially suicide.