Nice job with the Diva reccommendation. Excellent location, funky cool, easy size. etc. The $75 price may be a bit tough but you'll be close.
On your question: Chinatown for sure. Killer local, close to North Beach, Union Square, etc.
I know the Grant Plaza, I think it's Grant Ave & Pine, I lived Pine & Stockton for years. The local is cool but the hotel is 4 out of 10. It's OK but nothing special. The Ramada will be solid plus you are still close to clubs, shopping, cable cars, BART, etc. Have a blast. Stop in at the Stinking Rose on Columbus and tell them Tom from Venice Beach sent you, my wifes best friend owns the place. 🙂