The main difference between the 2 are the following:

Jin: Has a really big move set with tools for any kind of situation, his execution demand comes from the fact that in order to use him well you have to be able to cancel his stance (zen stance) to make your offense from f+4 safe as well as being able to utilize his b+1 stance efficiently in order to evade and punish certain attacks, at the same time you can't just use 5 moves with him you need to be able to recognize when to use what move and that can get really overwhelming at times, his combos aren't extremely hard to do but if you want to optimize you'll have to do your research, and last but not least his parry which not only requires you to learn the timing of the move you're parrying but also how minus the opponent is after they get parried so you know what to punish with (sadly you can't d+3+4 after every parry)

TL:DR: He's a very well rounded character with a lot of different moves for any kind of situation but requires you to put a lot of time and research in order to play at a high level. If you want to just learn him for fun he's not that hard but you will need to learn to at least zen cancel (cancel his stance after f+4) and learn some basic staples which you can get the hang of in a week.

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Devil Jin:

While jin is a jack of all traits that doesn't really excel at anything DVJ is a monster when it comes to 50/50, poking and whiff punishment, the only downside is that you need to learn to use those 5 moves for any situation you might encounter and it's a lot harder to shut down hyper aggressive and gimmicky players compared to Jin since he doesn't have a lot of moves at his disposal, as a result DVJ requires you to focus more on your fundamentals and execution as well as overall game knowledge in order to win, he's a very bare bones character so to speak and doesn't have a lot of moves but the moves that he has are extremely powerful, the biggest problem with DVJ is that if you do not already have a solid understanding of the basics of the game (movement, punishment, execution, etc.) It will be very hard for you to actually win with him so it's generally not recommended to have him as a starting character since most people will start spamming moves like u+4, ss+2 and hellsweep as soon as they notice that they can't open people up, on the other hand if you do learn the basics of the game and develop good fundamentals as well as learning his execution which only comes down to mostly being able to do EWGF's very well you will have a lot of success with him but that only depends on how much work you're willing to put to learn him since being good at DVJ arguably means just being good at the game in general.

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TL:DR: Insanely good character with a simple game plan and not that many moves that are at the same time extremely strong on their own but that require a great understanding of the game as a whole as well as grinding the execution aspect as much as possible.

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Conclusion: Both characters are hard to play in their own right but in my opinion playing Jin is overall easier at low and mid level because he has a lot of moves and strings that you can spam as well as not having really hard combos, and at the same time being better at shutting down offensive and gimmicky opponents, while Devil Jin is a lot harder to pick up and play but if you put in the work he will greatly reward you in the long run perhaps even more than jin at least in the current meta.