6' 180#, Athletic Build, 32x32 standard size in most pants.
I have multiple pants from both entities, and in a standard 32x32 size:
1. Fjallraven across the board fit absurdly tight through the butt and crotch, and ride a little low on the waist in general for my particular preference. I actually think the previously-described "thin" feel of the Fjallraven pants versus the Forloh pants is a plus, but I run incredibly hot and stuffy.
2. Forloh fit absurdly loose through the waist, and a little loose through the thighs. These are absolutely top tier quality pants, I would put the finish quality about Fjallraven.
I will also say, neither of them really bother me or get thought about after 15 minutes of "doing" whatever. They seem to do better once "warmed up".
Here in the PNW my go-to forestry pants in the West Side Jungle for the last couple years have been the Vidda Pro Ventilated after
@mxgsfmdpx recommendation in a different thread long ago. They replaced my Carhartt double fronts in that capacity. I picked up some BTM Pro's after
@Formidilosus write up about his gear and Fjallraven Keb's in particular, as I wanted a USA alternative and wasn't content with the fit of Fjallraven's in the upper region. They have replaced my Kuiu Pro Pant and First Lite Corrugate Foundry.
Having been on the receiving end of IP theft, I understand the general disdain for Forloh copying Fjallraven blatantly. Having been on the beneficiary end of patent expiration, I also understand imitation is a form of flattery.
You can't go wrong with either brand, both are top notch gear with their lemons and quirks, but you're most likely going to have to dial in the sizing either way. Fjallraven stores offer free tailoring if you buy in store, and then ship to your house. I have never been to a Forloh store to be able to comment on if they offer similar.
I recommend both brands wholeheartedly.