Just so you know, mathematically, the hp per level is superior by far to the other choices in that slot. I was talking about this in another thread I started before, but no one cared.
Here:
To those that don't know, armor and mr essentially increase your effective health by 1% per 1 point. Since I'm thinking about this primarily from a solo tank/bruiser perspective. If I'm Naut, who starts with 576 hp and 35 armor, my effective hp against physical damage is about 778. If I was to add 5 armor to that, it would be an effective hp of about 806, which is a 28 hp difference. And Naut has a decently sized hp pool.
For the third row, I also have a serious problem with the hp choice vs armor or mr. For starters, the hp choice works against everything. It also increases the usefulness of your starting armor and mr. In the Naut example, it would add 20 effective hp against physical damage at level 1 with his starting armor, and it scales up. There is literally no reason to ever pick the 5 armor or 6 magic resist because you gain another 88 effective hp throughout the game against physical damage from just that before even considering level up armor or bought items. With his max level up armor the scaling hp shard actually gives him 179 effective hp against physical damage. The direct comparison would be 5 armor increasing his level 18 effective base hp by 101. While you can get more out of the stat if you're buying large pools of hp, you're obviously going to more easily get more out of the other stats unless you have a special scaling like Rammus/Malphite or if you're Cho/Sion, who can infinitely stack hp.