Neither venue is brilliant for stuff in the 6's, but i think Tarn probably has a bit more than rodellar. And definitely more likely to find stuff ast the same sector as 7's and 8's. ANy 6's at rodellar definitely won't be at the same crags as harder stuff (certainlky not in the gran boveda).
Having said that, there's probably enough at rodellar to keep them busy fore a week, and i think overall it's a much better place.