There’s a good chance that the Cleveland offense will outperform the KC offense this year. Last year we were stuck with one of the worst offensive coordinators in modern football - who stayed with us an extra half year because coach catfish is gutless and wouldn’t get rid of his buddy. The lack of talent at O-line and QB didn’t help, but the offense was crippled by being badly designed in the first place.
Rob Chudzinski is the new guy, who ran the great Miami (college) offenses of the early 2000s and has been tight ends coach/assistant offensive coordinator of the Charges since. Bad first and second string QB mistakes have held the offense back score wise, but Cleveland still is #4 overall in yards per game in the preseason, topped only SD, DET, and ARI.
It’s mostly going to come down to when Quinn starts during the season. Everyone is so convinced that if you throw a rookie QB in, you’ll “ruin him” because NFL-level competitors are so weak mentally that if they get sacked once they’ll cry for their mommy and retire. But Quinn in the preseason, even after a holdout, is proving himself to be the best QB on the team. He’s only faced first 3rd/4th, and then 2nd stringers, but he can only excel in the situations he’s given, and he has.
In his first game, admittedly in garbage time against 3rd/4th stringers, if you exclude spikes during a 2 minute drill from being incomplete passes, Quinn went 13/16 for 155 yards, 2 TD, 0 int. In a much more meaningful scenario, last night against the Broncos in the third (most serious) preseason game, with a tied score, and a mix of first and second stringers in, he went 7-11 for 81, 1 TD, 0 int. Actually, he did better than that, because he threw a 30 yard +/- TD pass that the refs miscalled and because our coach refuses to ever win a challenge, he didn’t throw the flag. Some people think he didn’t do it in order to make Quinn look worse - they’ve already decided that he’s not going to start the season, even though “the best QB will be the starter”, and he doesn’t want fan backlash based on how good Quinn was looking. So if you factor that in (and it’s not a “if only the receiver caught it” hypothetical - it was a legitimate, complete touchdown pass that was ruled out of bounds), it was more like 8-11, 111 yards, 2 TD, 0 int.
They also signed the best guard in free agency to replace a big gaping hole at left guard, drafted the best tackle (hopefully elite but I have my doubts), and have star receivers recovered more from serious injuries. I’m biased, but there will be significant improvement. If I remember this thread, at the end of the year I’ll compare yards/game from either team and gloat as appropriate 
Edit: Oh, right, and to answer the original question, I’d probably take LJ. LJ scares me - bad offense, potentially overworked, lost a good (but declining) guard, but it’s hard to argue with the production that he’s constantly putting out. I expect him to decline, but to still be a consistent producer. But he’s still a more proven fantasy producer than Addai or Gore.