Well, I think Korean grammar was easier to learn for me because it's agglutinative. A lot of the grammar points are combinations of other grammar points. Also, words don't have as many changes as in Russian. You might have to add particles to nouns, but all that matters in that case is if the noun ends with a vowel or consonant. Unlike Russian there's no gender to take into consideration, the word doesn't change depending on the case, and you don't even have to clearly mark a plural word as plural most of the time.