H-Drol is much less toxic IMO. Having used both, H-Drol for 6 weeks at 100 mg a day does wonders, leans you up a bit and also increases lean muscle. I have dropped 10 lbs of good weight and increased in strength by about 20 lbs on each lift and have kept most of it after PCT.
M-Drol is awesome, and very toxic but the sides can be prevented with Liv.52 and Hawthorne Berry for blood pressure. Gains are phenomenal but they are difficult to maintain fully because its best advised to do only a 4 week cycle.
Also, if it's your first cycle, be hesitant to use M-Drol. I've used D-bol and H-drol before my first M-drol cycle and my immune system pretty much went down 3 days into it and I weigh 250. 10 mg is where its at for me, but everyone's different, just do your research because you only have one liver.