The strain we recommend is NEB Express. This is an E. coli B strain similar to T7 Express and BL21 (DE3), except that it lacks the T7 RNA polymerase (the pMAL vectors use the E.coli RNA polymerase). Another strain that has been used extensively is TB1 (NEB #E4122S), which is JM83 hsdR. There is nothing special about it with respect to the pMAL system, but it has given good results when considering plasmid stability, expression and purification. Other successful strains include NEB 5-alpha (NEB #C2991), NEB Turbo (NEB #C2984), and T7 Express (NEB #C2566) Competent E. coli. We also use other strains in response to a particular problem. One can start with NEB Express, or with whatever competent cells are readily available, and then try another strain if a problem with expression or purification develops.