Should I choose the SAM system or VPR system? Is it one better than the other?

Choosing which CRISPRa system to work with depends on several factors, as activation can be influenced by variables including: cell type, basal gene expression level, and method of delivery. In general, second generation Cas9 activator systems VPR, SAM, and SunTag all fall within an order of magnitude of each other with regard to fold increase in gene expression (Chavez et al., 2016). If you are just starting out with your activation experiments, we recommend using our CRISPRmod CRISPRa dCas9-VPR reagents, as dCas9-VPR only requires one component for activation, while SAM and SunTag require delivery of two components (Konermann et al., 2015; Tanenbaum et al., 2014)