Current FF wheels are far too weak to give any resemblance to real life wheel forces, so you have to find a compromise between FF quality and strength. I'd recommend a setting between 20 and 50% in LFS, depending on personal preference and car.
The problem with too high FF settings is that the forces quickly start maxing out, so the higher you set it the more the FF quality crumbles down till you end up with a purely on/off FF at some point. Higher FF settings give a more realistic force representation regarding strength and workout, but you lose a lot of fidelity and small details. It can also hinder your competitiveness with the bumps on the road having a larger impact on your steering angle, as well as lowering your steering speed due to FF motor resistance, making corrections harder.
It also depends if you mainly drive FWD/AWD or RWD cars - anything with driven front wheels has generally a much lighter FF than RWD cars do, allowing (or requiring) you to set the strength higher for a similar experience. Personally I use 40% for RWD, 50% for AWD and 60% for FWD cars.
