they are both excellent... helladrol will have less sides... both will give you great strength gains and size... i prefer helladrol because it is drier than diesel... they are both going to yield great results but personally, i prefer helladrol...
How about Diesel for a 4 week kick start for a Test/EQ cycle? I have 2 bottles of Diesel in my freezer that I am trying to figure incorporating into a nice mass cycle.
two methylated compounds is not recommended... it would just be very taxing on your liver, bp, etc... I would not recommend it as a stack at all... you could stack it with katandrol though and get some excellent gains!