I have a video I have put together using old DVD movies. I am using Premiere Pro to export a master to DNxHR.

I'm trying to figure out which DNxHR profile to use for the export. I'm not too concerned with file size, so I'm not even considering LB or SQ.
Thus, there are 3 options for me to choose from: HQ, HQX, or RGB444.
My understanding is that the difference between them lies in the color format.

The original DVD source is YUV 420 8-bit, which is what I understand HQ to be. But if I export as HQX or RGB444, will there be any advantages or disadvantages? While playing around with it, I did notice that exporting as RGB444 came out as a tad bit "darker".

As I mentioned, I'm not concerned about the file size (since this is all SD material anyway). But I would like to have the best possible quality for future re-encoding.