Francisco,
I am a bit late with a response, but here are my two cents.
As a matter of economics I use both styles.
If a slope is away from the curb, I use a regular 6" wide vertical curb (6" above grade and 8" below grade). The extension of the curb below grade can be deepened if desired to reduce percolation / infiltration from landscape irrigation from entering the base material. Over-irrigating is common. The below-grade portion also provides stability. Another less expensive option in this case is to pave, and then extrude a curb on epoxy adhesive. This is sometimes used, but more appropriate for long runs of curb due to equipment considerations.
I always use curb and gutter section where runoff will concentrate against a curb. Infiltration of water at the curb/paving interface will lead to water intrusion and premature failure of the base. Also, your curb and gutter slope can be in the 1/2% range, and that reduces the undulation effect in the drive aisles where the curb is parallel with the drive aisles.