Should I use IRES or 2A (and which 2A) in my polycistronic expression cassette?

When designing a gene expression vector to co-express multiple ORFs under the control of a single promoter, you can choose to place multiple ORFs behind the promoter, separated by linkers such as the internal ribosome entry site (IRES) or the 2A family peptides. For either type of linker, multiple proteins will be produced from a single mRNA transcript.