Bad area… you'll be stuck in the middle of nowhere at night and during the day it's crowded with tourists, feel like a demonstration.
Stay in Union Square as @LaffingBear bear said and folks will get to you and you to them easily. Besides you can come back walking from an outcall to the Castro.
I love the Park Central wit South view of Moscone Center, I've read you LOVE going downstairs to meet guys and that hotel requires a key to go upstairs, it's perfect for you. The Westin on Powell street is nice but make sure as a platinum you get a free upgrade to stay in the tower, the old part is close to the street and too noisy. The Meridien is also a good choice.
Avoid it!
One more thing, make sure to go up and down the streets to keep that butt in shape! Free exercise.