Korean skincare has made a huge name for itself because of the literally glowing endorsement of pop idols, while Japanese skincare is famous for the science, technology, and fine detail behind every product. That's not to say that Japanese skincare is better than Korean ones - in fact, my personal experience with the latter has been quite positive. I'm just saying that these categories became popular around the world through different means.
The question: is there actually any difference between the two? Yes, as a matter of fact. First observe what the two countries consider as ideal beauty. Japanese love soft-looking, petal-like skin - matte yet plump and healthy as a baby's bottom. The Koreans love glowing, truly radiant skin that looks so young you can mistake it for a little girl's.
I've tried lots and lots of skincare products from both countries and I have observed that no matter what the skincare line is, the effect is consistent with each country's definition of pretty. Japanese skincare gives me soft, matte, translucent, and plumped up skin. Korean skincare on the other hand gives me glowing, creamy skin that looks like it's lit from within. Korean skincare also has more steps - some reaching up to 7-8 products in the sequence including masks - while Japanese products cover a simpler daily routine. Convenience is key!
Instead of having several steps, J skincare caters to specific needs even within one skincare line. For example, you can find two different moisturizers or even facial washes in one collection. The active ingredients and function are generally the same as the rest of the line but with a more targeted response to certain skin concerns.
So, which is better: Korean or Japanese products? I think they're both excellent, generally! They're made for us Asians and our climate, so it's pretty hard to go wrong. Use whatever works best for your skin and the look you prefer. However, if you want to get the best possible effect, I do recommend using only products from the same line/collection instead of mixing it with your other skincare brands. The result is more consistent, I've found!
Hope this helps. Do you have a preference between Korean and Japanese skincare?