From a quick google maps browse, looks like you could walk to the event center from the Hyatt Regency on Barton Springs, the Embassy Suites on S Congress, or the Extended Stay on S 1st.
I've only been to the Embassy Suites out of those, and it's pretty nice. Amazing location for walking downtown or exploring south congress.
Hotel St Cecilia it's gorg, Hotel San Jose is also pretty neat. But if you're traveling for work and your job has some specification on the type of lodging, I'm not sure if they'd fly.
The Hyatt Regency on Barton Springs is a good central spot and the Embassy Suites on S Congress is also a good area to walk around, so if you're not looking for whimsy I'd prioritize those first.