Nickel vs Cobalt. Which metal is best for IMAC?

Immobilized Metal Affinity Chromatography

Metal Ion Nickel or Cobalt
Ligand IDA (iminodiacetic acid) and NTA (nitrilotriacetic acid)
Capacity Ni-NTA > Co-NTA > Ni-IDA
Affinity Ni2+ > Co2+
Specificity Co2+ > Ni2+
Imidazole Elution 250 mM (Ni) > 150 mM (Co)
EDTA/DTT Resistance NTA > IDA
Re-chargeable NTA > IDA