Most experts agree that it depends mainly on intended applications, as well as the nature of your materials. For example, if sequence accuracy of the amplified product is crucial, look for high fidelity enzymes. These are also appropriate for applications requiring amplification of especially long DNA targets. “Some amplifications are challenged by DNA regions with repeat sequences, such as TA repeats, or challenging secondary structures, such as GC-rich repeats,” says Majid. “Here you need robust enzymes with buffer conditions to overcome template challenges.” New England BioLabs’ product manager Fiona Stewart agrees that “it [is] challenging to obtain robust amplification of GC-rich regions, and also retain a high level of fidelity in amplification, since high-fidelity polymerases are more susceptible to difficulties in amplification of GC-rich regions.” New Englands Biolabs offers the new Q5 High-Fidelity DNA Polymerase to overcome this challenge, and EMD-Millipore offers KOD Xtreme™ DNA Polymerase.