Atk/def/Sta explained alittle more in depth plz?

atk is more important in terms of cp, so #2 would be better if you values atk a lot. High IV of a certain attribute does not mean a pokemon is a good attacker or defender since IV only affects the real value of atk/def/sta very small. If you are looking for good attackers/defenders, you should look at their moveset first.

The way I understood it attack is the damage the Pokemon dishes out and defense the damage it suffers. So it applies to attackers and defenders I think.
But in the example you give the difference will be pretty minimal I guess.
If I am evolving and hoping for a defender I always use the CP calculator and go for the one that will give me the highest CP as that seems in practice to be the most important factor for a defender. And ironically that is often the one with the highest attack.

Without wanting to give mathematical details i can provide a rule of the thump:

The IV value, that boosts the weekest stat (and thus provides the highest relative (percentual) increase) is most important.

Two examples:

Cloyster has moderate Att-, very high Def- and low Sta- stat. Most important is a high Sta-IV, followed by Att, while Def is least important.
A Sta-IV of 15 gives 15% more battle performance (damage delt until pkm faints) Att-IV of 15 gives something like 9% Battle performance, a Def-IV of 15 gives less than 5%.

Chaneira has a very low Att-Stat, Def is moderate, Sta is huge. Here Att-IV is most important; Att-IV 15 gives 25% battle performance, Def 8%, Sta only 3%.

Besides the examples worth noting is, that Att is fully wighted in CP-Calculation, Def and Sta only square rooted. So Att-IV has almost always the greatest impact on CP (with all consequences for gym-Placement and Prestiging)