The adjective かたい (solid, hard, firm), With which of these Kanji Is it often written?
With which Kanji is it more often used?
硬い / 硬い / 堅い

Question

Answer

I guess the most frequently used kanji (かたい）is 　固い　（⇔　緩い　（ゆるい））.　From these two, I would say 硬い, but depends on the sentence, we change the kanji. So it's hard to say which one is the most.... Btw,  硬い　⇔　軟らかい　、　堅い　⇔　もろい　this idea helps me to figure out which one to use. Hopefully, this was helpful.

Answer

It's antonym.

「固い」⇔  loose
「硬い」⇔  soft
「堅い」⇔ fragile (or weak)

Answer

硬い」と思う。