ES3 is very linear, except for the slight sub-bass boost. It is musical and has no treble harshness, however. SM64 sounds too romantic, too lush. It has a huge 5 kHz dip that makes everything sound very smooth. Is it a bad thing? No, it's still detailed and technical but it's also very lush and romantic sounding so it's not good for monitoring. ES3 is fun mixed with analytical so it's good for both listening pleasure and monitoring.
It is worth noting that ES3 sounds closer to K702. SM64 is like HD650, even more laid and smoother sounding (maybe like Audioquest Nighthawk but I haven't heard that HP). ES3 is closer to AKG house sound. I would say ES3 is still smoother (but no less technical) compared to AKG house sound, however.
Earsonics Velvet is the best in Earsonics line for bassheads. It has so much bass in warm mode. Mids are thinner compared to ES3 and SM64. It is more expensive than ES3 though.