I can for sure say after some hefty 100 hours into Assetto, assetto's force feedback is more detailed and gives a better raw feeling about the car's suspension when going around a turn, and I can tell when the back/front tyres are about to slip.
However since its a fully focused racing sim its driving doesn't feel relaxing at all unlike LFS. after one hour or two I'll be tired from constantly dealing with the heavy steering while I can drive for HOURS or a whole day in Live for speed, but don't get me wrong it can be as intense at times specially racing for a good amount of laps in a GTR...in a TRACK
Overall opinion? Both do great at what they are, plus assetto does have some really good engine sounds(real licensed cars duh), one of the reasons I still play it as well, I wish Live for speed had a better engine sound system in that regard(sorry CSR is too much work for me
).
But as people are saying, with this future update Live for Speed will be at its best shape, matching assetto graphical and possibly feel-wise, but its relatively easier to overcome a sim that was finished some time ago, still a good sign, Live for Speed is going somewhere, and it'll be always my all time favourite sim for long driving sessions