I think that it is best to stick with the methylated form of Vitamin B12 (also known as methylcobalamin).

This is because many people have mutations in a gene called MTHFR which means that its encoded protein is not very active.

The full name of that protein is methylenetetrahydrofolate reductase. It is an enzyme which, among other things, converts Vitamin B12 into its active (methylated) form.

People with these common mutations are not able to convert Vitamin B12 into its active form very well.