One good reason for staying away from toroids is that you can't put gaps into them because they are one solid lump. However, with EE ferries you can easily sand down the centre limb (or put thin spacers in) and make fairly accurate gaps but, why might you want to do this I hear people say.

It's all about maximising the power throughput for a given core size and operating frequency. Sometimes (quite often in fact), it is necessary to make a small gap to reduce the permeability by say 10 to 1. A reduction of ten means you need more windings to obtain the same inductance but you only need the square root of ten more windings. This means that you can deliver a bigger H field to the primary and have less core saturation.