I am undecided between M and L - my jeans...
I am undecided between M and L - my jeans are 33", but if I measure my waist it's way more than 33", closer to 36". Now, I also got Arcteryx Gamma AR pants, and couldn't fit inside M size (just slightly too tight) - anyone know if the measure from the waist is the same between these two pants? As I am slim, I would prefer size M for less baggy pants, if they would fit from the waist.
The size of the two pants should be the same. The one difference with the alpha is the fit in the waist. The alpha comes with an athletic fit which allows it to stretch, compared to the Gamma pants which have a trim fit.
Based on you having a 36" waist I would go with a Large. Also if you are tall ( 5'11 and up) you should go with the tall inseam, but if not just go with the regular inseam