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
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).
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
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