Everyone has an opinion on this question - I know!
And I've stayed off site and on site for runDisney races before; but, I always come back to suggesting staying on site because of the benefits of bus transportation to and from the Expo, to and from the race, and Disney resort benefits of Fast Passes and Extra Magic Hours.
However, recently Disney has expanded their Fast Pass 60 day early registration and Extra Magic Hours to a group of Disney Springs Resorts. That sounded really appealing to me. So, I split off my stay for the Princess Half and stayed 2 days at the Hilton Buena Vista Palace just to test the water.
I spent the rest of my stay over the Half Weekend at the Contemporary.
I looked at Room Rates, runDisney Bus Transportation, Park Transportation and Extra Bonuses ....
Let me know what you think - and send me your on site / off site questions!