3 cross pattern what's the right way?

The second variant (where you lace the outer spokes under the inner spokes at the last cross, I'll call it cross-under lacing in the following) has a slight wheel stability advantages:

• When you transmit torque over the spokes, you are putting tension on one half of the spokes while removing tension from the other half.

• The cross-under couples the tension of one leading spoke with one trailing spoke.

• As such, the cross-under reduces the likelihood of one spoke loosing all its tension during acceleration/braking, and thus serves to make the wheel more robust.

On the other hand, the cross under has a significant wheel-building disadvantage:

• Since it couples the tension of two spokes, you cannot adjust the tension of one spoke without affecting the tension of the other.

• Since two spokes are coupled at the cross-under point, they cannot vibrate individually. This makes it impossible to equalize spoke tension by ear.

• The cross-under simply makes wheel building a bit harder.

Since I personally prefer to tune my spokes by ear, I never use a cross-under. Other people have other preferences. Afaik, factory laced wheels often come with cross-under, I guess that's because they have the equipment that makes cross-under lacing easy. And because such wheels are known to be a bit more robust, they sell better.