Okay.. Both will be reborn in the same world(Random cultivation world...no gu or magic world) with their experience from the last world(gu and magic world)with no powers....Without their A.I and cicada gu.....Who will survive and be more successful(in cultivation and sh!t) in their Life?? No plot armor!
Leylin was never not winning and got everything he wanted and more. Fang Yuan wasn’t always like this. Through hardships, he was made this way. Even then, he doesn’t have everything he wanted. He had to compromise at some places. Leylin is the most successful. Leylin is far more dangerous than Fang Yuan in a whole new world. He would adapt much more quickly and derive whatever he wanted from lesser things while Fang Yuan would be fighting for greater things.
Fang Yuan easily. Everything Leylin achieved could either be traced back to his A.I. chip or his bloodline. From memory it was the chip that also stored all of his knowledge and was the main component in his alchemy. Fang Yuan on the other hand had experience with two different lives both of which he climbed up through his own will. He has experienced failure but more importantly how to act in failure to survive. He has higher chance of survival in this new world without his powers from the old(knows how to fight, battle tactics, how to survive with nothing). On the other hand Leylin without his magic or bloodline would not have as high of a chance. Sure he is from a knight family but I would say is not as experienced as Fang Yuan at fighting without special powers/abilities. Also not sure how well he would survive if the start location is in the middle of a forest or some other dangerous environment.
Well I didn't spend much time thinking but Im going with Fangyuan, he's already experienced a sort of cultivation world and knows how to behave also Its been a while since i read warlock of the magus world but i dont remember leylin using people often like without actually using them forcefully or their bodies for experiments, also the concept of dao and stuff still exists in the cultivation world not to mention all of fang yuans attainments,