There isn’t a lot of difference between the two as their protective qualities are pretty much the same. However, oil and varnish finishes require different types of maintenance. To get the most out of your floors, your decision should be based on the amount of wear and tear the floor receives.
Using a wooden floor varnish requires less maintenance, but you’ll need to have the entire floor resanded back to bare wood to replace the varnish when it eventually gets damaged. How long this takes would depend on the type and quality of the varnish and how much wear your floor is subjected to. It could be every year if you have pets, visitors, and kids running in and out all the time. It could be every five years or more if your home life is a lot quieter or if your floor is covered with rugs.