How FUN!!!! Here's my take... I don't know what your interests are so I might be off base. We like great hotels, bar areas and nightlife.
Dallas: downtown Hotel Zaza (Dragonfly) usually a good crowd at the bar area. Outside is a pool and more social activity, Crescent, just a nice hotel with great spa and the W Ghost Bar WAY up on 33rd or so floor with ledges outside to look down. Great view of city and good nightlife. We also like Nylo in Plano which is like Zaza and the outdoor area is much larger. Loft 610 in Frisco/Plano is also a fun spot. I've heard that Sambuca will be opening up on Sept 3 at the Shops of Legacy where Martini Park used to be.
Austin: I'm not that frequent of a visitor but LOVE 6th street
San Antonio: I enjoy the riverwalk, restaurants along the walk and people watching. Stay at one of the hotels on the riverwalk. Marriott has a nice one and I think another one is either Hilton or Hyatt, not sure.
Southwest has some great airfares and you can hop down to Austin or San Antonio for a great price.
I head to South Beach in Miami for girls weekend. I love that place and it is full of nightlife and 24 hr fun. I fly to Miami and take a cab to Ocean Dr, whereever I am staying. Cab fare is around $40 each way with tip.
Whatever you choose...HAVE FUN!!!