In which type of reproduction is there a more chance of variation?

Variation means a change in the phenotype of an individual as a result of alteration in the genetic makeup. 

This is more pronounced in sexual reproduction when the characteristics of both parents are inherited by the offspring during fertilisation.

Binary fission, fragmentation, and regeneration are different types of asexual reproduction. Since there is only one parent involved in the process of reproduction, there is no mixing of characters and the offspring produced will be the exact copy of its parent.