OP, you're going to have to give us more detail about your butthurt.

It actually sounds more like a saddle issue than an underwear/padding/chafing issue, given you're saying "my butt hurts."

Saddle are a particular and highly personal topic. Myself, It took me months of trying saddles to find the right one, and once I did, I never had any discomfort of any kind in the nethers, even having been off the bike for 6 months last winter. (Prior to that, my butt had to "toughen up" at the beginning of the season.)

But just to echo people above: no underwear for any distance over 20 miles; yes padding; medium hard saddle.