Hello.
i ve' been reading the properties of some metals such adamantite, cold iron, mithral and stainless steel, they are all so good that it's hard to decide.
This takes me to another question: is it posible to alloy different metals to mix their properties, if yes, wich are the restrictions?
And so...
What is your favorite material to craft metal weapons? and why?
is it posible to alloy different metals to mix their properties, if yes, wich are the restrictions?
No. The rules for special materials state that only the benefits for one material apply. The only exception is a double weapon where each end is a different material.
What is your favorite material to craft metal weapons? and why?
Mostly, it depends on the campaign (and the expected enemies). A campaign like the Wrath of the Righteous AP (demons as a common foe) means you should emphasize cold iron weapons more than normal...
In general, a well-prepared character should (eventually) have an adamantine weapon, an alchemical silver (or mithral) weapon, and a cold iron weapon. This includes ammunition (cold iron ammunition treated with silver weapon blanch is a pretty inexpensive option) and a back-up weapon such as a dagger (masterwork cold iron dagger is 304 gp, mithral dagger is 502 gp).
Usually, you should strive for your primary melee weapon to be +3 holy adamantine (additional bonuses/abilities to taste) to deal with the most common damage reduction types (+3 enhancement bypasses both cold iron and silver, holy for DR X/good, etc. You should also probably have at least one option for each of the bludgeoning, piercing, and slashing damage types (dagger can be used for piercing or slashing, a battle aspergillum does bludgeoning, etc.).