I have both the SRH440(with 840 pads) and ATH-M30s. They're both great value sets. The M30 has better isolation, and is lighter. The SRH440 is better for traveling and has a removable cable. I find the SRH440s are heavy on my head and not as comfortable. I do find the SRH440s sound better though. They seem to have more range than my M30s. The biggest perk about the M30s is I can listen to them at a louder level and there is little to no leakage.
For comfort and isolation get the M30. I found my M30s sounded even better after I hooked them up to a USB DAC/Amp.