As terminal 3 and 1 (*Alliance terminal) is not operating at the moment and a lot of *Alliance flights is from T2A and B (I presume that OP is connecting to *A within Schengen?) the CDGVAL would be a poor choice. I even suspect that walking would be faster then the bus with a connection from 2A to B, but the fact that you don't have to bypass immigration in 2A when taking the bus, would make me personally prefer that route.