Toroidal and E core transformers don't behave much differently in this application, so I wouldn't get hung up on what transformer you go for. If you are into audio amps, the toroidals generate less of a stray magnetic field which can mean less risk of hum.

BTW, if you are bothered by the Bees Nest (TM) fans in the LiChuan servos, you can replace them with pukka Papst / NMB / Sanyo etc fans from CPC. I did this on mine and it has made the noise almost bearable.