Hannibal, the choice really comes down to how good the teams are today and what you think you'll be able to do with them in the next few seasons.
If it'll take a couple of years to rebuild and make the postseason I'd take the baseline C team. The D baseline prestige team would come down if you missed the postseason for a few years. But on the C baseline prestige team, you won't go down much more if at all and when you do have a good season or two you'll come up farther, quicker.
The tradeoff is that it'll be a little harder to recruit at the team with the current D prestige.
If each team is good enough to win now or next season I'd just take the team currently at C as I assume neither of these is your dream job and you'll be looking to move on again in the next few years.