Caulk or not to caulk?

What's the best filler to use around the edge of a upvc window where the pcv window meets the wooden frame? I used caulk a few of years ago but have just spent a long time cleaning the upvc frame and scraping off all the caulk which had turned yellow. Is it better to use a bigger bead? Could I mask the window then caulk around the edge ensuring all the caulk is painted so it doesn't turn yellow.
Thanks in advance for any help

Caulk is designed to be painted over, isn't true white and yellows.

Use white silicone.

I always use masking tape, if I'm using Caulk or Silicone. I find it leaves a much neater edge.