The one on the right is best, however, if you can consider having existing hardwood sanded and stained to match new hardwood you will probably be happier. I’ve done both in different areas of a previous home. Bedrooms work best with your plan because they have a door way to help with the transition.

You have site finished oak. I would get more oak and have it finished to match. Age dependent you may want to consider having it all refinished. The prefinished you have there will look like a miss. Between the colors and the microbevels it will not be a good look.

I would install wood flooring that matches.

IMO unfinished for the new and stained to match the old

Put unfinished red oak down and site finish it with oil base poly. Keep it simple.