HP is always the correct choice because it is innately needed for survival. By decreasing the amounts of HP on items, you do not solve any problem, you simply shuffle. In general, there are only two modes of HP items: useful and useless.
They are useful when they enable you to live long enough to run away or to kill somebody. They are useless when they do not. This is a generalized statement, as there are always edge cases (ie, the "sacrifice" which sometimes does happen in order to get a sweet triple kill or something).
A basic equation is this, given HP items itemN, itemN+1, itemN+..., if the cost of those items is less than the cost of the same number of items that do the same amount of HP as damage, then the HP items are a better buy. The reasoning is this:
if we have 6 items, 3 HP items and 3 Damage items such that
HP items cost 800, 900, and 1k gold and the amount of HP gained from the items is 400, 500, and 600 respectively for a total of 1500 hp.
Damage items cost 900, 1k, and 1.1k gold and add bonus damage of 25, 45, and 65.
The question of which set of items is the better buy, all other things equal becomes a question of either out killing or out living for the same amount of money. That is to say, if you buy the damage items, can you kill somebody that bought the HP items before they kill you. Or, likewise, if you bought the HP items, can you kill somebody that bought the damage items.
The problem of choice is that typically the case is that buying the HP items does mean you will be able to kill somebody first. And the reason for that is because of poorly scaled weapon damage items not affecting the DPS in a great way.
Ie:
Players start with 100 dps and 2k health. In this state, Player 1 would need 20 hits to kill Player 2 (assuming no HP regen).
Now say, Player 1 decides to get 20 more dps, player 2 decides to get 500 more health. It takes Player 1 21 hits to kill Player 2, while it still takes Player 2 only 20 hits. This means that the HP purchase was a better purchase.
This is the fundamental problem, expressed in a very simple example. The damage gained from dps increase has to offset the HP gained from an HP increase of the same gold expenditure, otherwise the items are not balanced and they CAN be reduced to a pure math based choice.
So,
Items HPItems = HP_Items_You_Want;
Items DPSItems = DMG_Items_Used_Against_You;
Items AlternateItems = Some_Other_Set_Of_Items_You_Are_Considering;
if(cost_of(HPItems) <= cost_of(DPSItems))
{
if(HP_Amount_of(HPItems) / DPS_Of(DPS_Items + Base__Opponent_DPS) > HP_Amount_of(AlternativeItems) / DPS_Of(DPS_Items + Base_Opponent_DPS))
{
// Then buying the HP items is the right choice!
}
else
{
// do something else, you are mathematically going to get ganked
}
}
Making damage items have an effect on skills is probably the best solution, in all honesty. Making skills be skill_damage + current_autoattack_damage would make the damage vs hp choice much more interesting and robust.
