Luke Skywalker (RotJ) vs Kylo Ren

All-out

Luke easily

I need to think about this one for a moment. 

In terms of raw power, RotJ Luke and Kylo Ren should be pretty comparable. Both have been directly and repeatedly compared to Darth Vader, which makes sense considering their bloodline. Their displayed Force feats are too different to reliably compare. 

Luke's two best feats so far in Canon are when he shook a whole Star Destroyer with a Force push in a moment of desperation, and when he TKed the controls out of the grips of 17 TIE pilots simultaneously, leading to the destruction of the entire Squadron. That last one is one of the best feats of TK control in the entire Star Wars Canon right now, but it's been pointed out that he may have done so with the aid of the Dark Side, due to his mindset at the time. So, Luke's two best feats were due to either desperation or unbalanced emotions, but the scope of the feats is still extremely impressive.

Kylo Ren's best Force feats are a bit smaller in scale, but nonetheless impressive. He toppled a massive statue, after ragdolling two of Luke's Jedi Padawans, displaying a great deal of control over the raw power at his disposal. However, the magnitude of that feat is still small compared to Luke's Star Destroyer feat. Kylo Ren has also dominated a First Order officer with TK from a great distance while communicating with them through a holomessenger, much like when Vader was Force choking admirals on other Star Destroyers. This is another impressive control feat, but it doesn't really tell us much about how effective he might be against another Force user.

Honestly, until the Star Wars 2020 comic series continues and shows us more of Luke's post-ESB training, I'm inclined to give Kylo Ren the edge when it comes to the Force. He's been repeatedly shown using the Force against other Force users, during the Rise of Kylo Ren comic series. He's also more consistently been portrayed having control over his power, while Luke's feats tend to be erratic. Not to mention Luke just isn't inclined toward using the Force in combat, as we've repeatedly seen in his fights against Vader and against Sergeant Kreel. 

As for swordsmanship, Kylo Ren again has more displayed showings, while Luke's are a bit more impressive. Kylo Ren was able to duel three of Luke's trainees at once, though not without taking some wounds and being forced to give ground. Kylo Ren is also confirmed to be Luke's best student, and appears to be capable of defeating any one of Luke's apprentices in a fair fight. He performed extremely well against several Praetorian guards, though ultimately one got the better of him after he'd been disarmed. I won't go into his duels with Rey, as she has no real measurable scaling, and his first duel against her had too many extenuating circumstances.

Luke's dueling feats are a bit more narrow. He was clearly superior to Sarco Plank in The Weapon of a Jedi, and seems to have surpassed Sergeant Kreel as a duelist according to Thane Markona in the 2015-2019 Star Wars comic. He also put up a good fight against Vader in ESB, though was ultimately no match. And by RotJ, he was Vader's equal as a duelist, and arguably had surpassed Vader. This last feat is the only one actually noteworthy, but it alone should be evidence of Luke's superiority to Kylo Ren as a duelist. 

In the end, I'd say this fight would be extremely close. Luke would put a lot of pressure on Kylo blade-to-blade, but if Kylo is able to disrupt Luke with his superior control over the Force, he may be able to take the win. 

That being said, once the 2020 Star Wars comic continues, I'm sure we'll be getting more feats for Luke which will likely put him above Kylo Ren. Charles Soule likes to go big with Force feats, as we've seen from his Vader run, The Rise of Kylo Ren, and what we've seen of the 2020 Star Wars comic so far (giving us the 17 TIE feat). If this trend continues, Luke's likely to get some more high-end Force feats, which will likely settle this debate in time.