Hp or defensive EVS which will live longer

Question

Im looking to create a pokemon that takes the most hits possible.

How should I EV train 252 into Hp Or 126 +126 in Sp. D, and Def?

Also how is the stat calculated with the evs?

Ex: added to the base stat, or multiplied by base stats

Comments

For every 4 EV points your Pokemon gets, it raises the corresponding stat by one. Also, you would want to out 128 EVs in defenses, as 126 wasted a few EVs.

Answer 1

EV adds to your stat, not multiplying like nature.
So if your pokemon has lower HP than other two(ex.Shuckle),
give 252EVs on HP and rest on Def and Sp.Def
So give your EV on the defensive(HP/Def/Sp.Def) stat which it lacks on

But there are some exceptions.
for example, for eviolite dusclops or dusknoir that has pain split,
you should give 252def and 252sp.def, since painsplit is better move if you have lower HP

and for blissey with counter, it is better to give 252 on def(since it can be OHKO)
and 252 on HP(for counter)

The stat is calculated by
4EV=1stat point
when it reaches lv.100
so it is best to give your pokemon's EV that is multiple of 4, or it can be wasted