I would go with the second one, “My interest for philosophy sparked after…” just sounds more…interesting and dynamic? I think you should mention when and how your decision solidified and your experience in the field, especially if you have plenty to emphasize, and go into how it shaped you as a person and helped you grow into a person. Give examples.
I hate personal statements because I hate having to sell myself. But it’s good practice for the future, I guess.
My BIL showed me his personal statement, he got into UC Berkeley for EECS and it started off pretty much like “I intend to major in electrical engineering. My interest in the subject began…” and it was a little dry and boring to be honest, but he was accepted. Then again he had incredible GPA and stats, so I don’t know.