Max Block is better depending on the life you have.
Also depends on other stats.
If you have under 1k life. Max Block may not be the best option.
If you have under 25% DR, Max Block may not be the best option.
If you eventually farm up a CTA. Max Block would be more viable at that point.
If you had over 25% DR, Max Block would be viable, assuming you have max res.
Untwinked, pure vita might be fine. But Max Block is better than pure vita once you start to get geared.
Monsters scale crazy as you go on, especially players 8.
Also depends heavily on the shield you are using. If you get your hands on a stormshield, most of the time you want to go Max Block because you already have 35% dr.
And I can tell you now against the snakes in Nihlathaks lair, the only thing that can save you is a max block and damage reduced by flat , because flat will reduce the damage more than % because they do a lower amount of damage at a glitched rate.
You also can't dodge their shit with high defense because the damage comes from the poison and also they can do upwards of 4k health easily in a group of 4-5. I've tested before with a 95 poison res champion with like 7k life. Let the snakes hit your for 3 seconds it went down to 1/4 in 3 seconds. The reason for this is because the damage is bugged and the damage you take in poison is not reduced by your poison res.
Seb I agree maybe max block isn't good for you now, but the better your gear gets, especially if you obtain a CTA, Max Block will always be better than pure vit in those cases.