Choosing where to buy the smart phone and provider

Hi,
I am going to live in Guilin upcoming month but before I will go to Kunming for few weeks. I am thinking to buy a smart phone and sim card but it has made me questioning few things as follow:
1. should I buy the smart phone and the sim card in Kunming or in Guilin?
2. which sim card/provider is better for data service?
Thanking you in advance for any feedback.