I wouldn't hazard a guess as to a percentage. However, I would say that any owner of either commercial or industrial properties would be unwise to use either a pure NNN lease for retail holdings, or an industrial lease for industrial assets.
It is more normal in the industry to use NNN leases for many reasons, most of all a definite sharing of costs, rather than a projected and included sharing of costs as in a gross, or modified gross lease.
This answer is likely more general than you wanted, but it is specific enough for me to always recommend NNN leases for retail and industrial properties, unless special circumstances warrant otherwise.
Onward and Upward!
CA DRE 544165 (one of the oldest active licenses in CA)
AZ DRE 641305000
Mar 1, 2013