Episomal vectors and Sendai virus are perhaps the two most common vector systems currently being used. Both systems work well and have been adopted by numerous labs (see Schlaeger et al., Nat Biotechnol, 2015) but preference will typically come down ease-of-use, cost, and downstream analysis for vector clearance or integration. And yes, we have a protocol for reprogramming using episomal vectors, which you can access here.