Should I Transcribe Episodes or Write One-shots to Help Write Accurate Character Voices?

I feel like the title says it all, Should I Transcribe Episodes or Write One-shots to Help Write Accurate Character Voices? I want to write a long fic for one of my favorite fandoms but I'm so mortified at the idea of accidently writing something out of character or cringe so I'm wondering what you guys think would be better to get practice in before writing my long fic.

Edit: For clarification the transcriptions would be 100% private and for personal use!