2.4Ghz is more stable, has longer range, and is less sensitive to obstructions in the building. Give it a try.
I would say that it depends. If you live in a city chances are the 2.4Ghz band is very busy and your network stability will be affected negatively. In this case 5Ghz may be the better option. My current wifi setup is 5Ghz, it is fast and it is rock stable.
But there can be many reasons for unstable wifi. A little anecdote: my old ISP shipped a ZyXEL wifi-router with a broken firmware to all its customers. The wifi-router supported 5Ghz wifi and it worked great, except the 5Ghz would stop responding after a random period. Devices connected to the 5Ghz network would just "hang". The issue was acknowledged by ZyXEL and solved in a firmware update, but I am not sure if the ISP ever managed to deploy the firmware update to all customers.
