For me, it has to be “Old Boy” which is originally a Korean movie but the US version sucks so much that it remains incomparable. Another contender is “The Ring” again a Japanese movie (the ending differs between both versions, as the original one refers to the protagonist’s father sacrificing himself but the remake states that the cursed tape is being sent to someone else, passing the omen towards another stranger).
One of my favorite movies of all time is “Let the Right one In” (“Låt den rätte komma in”), a Swedish romantic horror film. There is an American remake called “Let Me In”. The pacing, mood, and atmosphere of the remake don’t even come close the original. I believe the American versions of foreign films are often more expensive, polished, and with better actors, but I don’t need that to enjoy a film. One recent example is “Bugonia” which was nominated for 4 academy awards and is very well made, yet I enjoyed the Korean original “Save the Green Planet!” just as much.