Sexual reproduction is more likely to increase genetic diversity because every offspring has twice as much genetic material to pull from when being formed compared to the one set of genes in asexual reproduction. There is also the differences between mates that can increase genetic diversity as well if many different mates are mated with.
Asexual reproduction typically happens more quickly, however, because an asexually reproducing organism does not have to bother with finding a mate, courting and allowing time for the genetic material assimilate, they can just reproduce and all of their genes are utilized in the new organism rather than just half.
The whiptail lizard may reproduce either sexually or asexually depending on the environmental conditions.