NAD and the 'precursors' to NAD such as nicotinamide and B3-niacin

I'm having to reconsider my NAD strategy. Al Sears' NAD is too expensive, LEF's NAD is difficult to get and NAD is still debatable. However, the precursors to NAD seem to me to be more viable.

1. NR, nicotinamide Ribose
2. NMN, Nicotniamide Monocucleotide
3. Niacin B3