[James2001]

I always just keep everything I digitise interlaced, then let whatever player I use deinterlace the file. The deinterlacing in these types of video rendering software is often flawed some way, and then when you render it as 50p, any deinterlacing artifacts are baked into the file, so it's best to at least keep a file in the proper interlaced form even if you are making 50p copies, then you can also go back to it later if you improved software. Similar with scaling to different resolutions.

I do make 50p copies of files when I share them online because you can be pretty sure different hardware and software that people are using will handle progressive video properly (unlike interlaced files where you get all sorts of wacky variations in how it's treated), but I always keep the original 50i files.