I think blm is probably the least demanding that you dodge WHILE casting... As you largely can't. Summoner is a wee bit more mobile in that they have more instant cast options. BLM's key to success is learning the most advantageous positioning that will result in less overall movement and maximization of casting time. And learning to use procs well. My dps main is a blm, so I could be wrong about this, but smn appears to be more versatile, if a bit more complicated.