webtoon is still not ended. i personally like webtoon more. the characters and their past is dealt really well in webtoon. but it is still not complete and its hard to find translations. so if you are fine with that start reading webtoon. but drama adaptation is not bad

I agree with both posters above me, I'm up to the end of season 3 (ch 183 ) in the webtoon and it's one of my favorite webtoons of all.   I haven't found translations for season 4 yet and that is current and ongoing.     The casting of this is great and the first 10 or so episodes follow along well with the story and then I'm not sure as the webtoon is ongoing and because of that   I don't know if some of the things in the later part of the drama will ever happen in the webtoon since it's not finished and the drama made an ending.   That is my reservation,  But it's always like that if you read the book and then the movie is different....   So I would watch it first and then read it and that way you will be adding to your experience instead of taking away from or comparing.   The webtoon is much longer and more complex and definitely a great read, but I still think you should watch first.