Chessable or Chess King?

They are very different and I'm sorry, but if you are serious both are recommended.  Chess King is set up like a game where you need to solve tactics or win handicap games against an engine.  I've probably gotten to level 22, 23 a few hundred times; it becomes a little like playing Solitaire after awhile.  Chessable presents a series of courses with a learning and then a review/testing phase.  There are some basic tactics courses, but opening study seems most popular.  The trick with Chessable is to start over on a course periodically to clear the books.  There's a course on 37 basic checkmate patterns that I can rip through pretty quickly now.  Anyway, they're both pretty cool.  In truth, if you're just after tactics training, chess.com is actually better than either of them.  You might want to try a month of Diamond with unlimited practice and see how that goes.  The ability to study specific tactical motifs (in unrated)can really help.  I use all 3, but I'm so old I'm just trying to slow the process of getting worse rather than trying to get better...LOL.  Hope that helped a little.  Good luck!

Can't believe I didn't mention GM Wolff's tactics courses over in the Lessons.  Superb treatment of all the tactical motifs.  Another reason to maybe try a month of Diamond.

I'm not familiar with Chessable, but all the major chess education companies (eg. Chessbase), fill it's own niche.

I do have nearly all of Chess Kings stuff, and I highly recommend it. But comparing it to another highly rated company that has training stuff is just comparing apples and oranges.

Chess King fills a niche for doing chess problems, but at the end of the day, it should be a tool in one's toolbox. Other companies like Chessbase and Chessable are other tools in your toolbox.