Hi there,
The choice is yours and although the AMI BIOS is still being worked on it is pretty stable otherwise Gigabyte wouldn't release it. If you are not overclocking then it should be fine but, if you are looking for improvements from the Award BIOS for O/C'ing then you maybe disappointed as this seems to be the area which needs fine tuning in the AMI BIOS.
You can't update to the AMI BIOS in the usual way and it is a little more complicated. You need to create a Bootable USB pendrive and then use the FLASHEFI.EXE program in DOS to flash the BIOS. You only have to do this for the switch from Award to AMI BIOS though and once you have done it future updates can once again be run using QFlash.
There are plenty of screen shots of the new AMI BIOS on Gigabyte boards and I prefer it to the old Award BIOS but, it is different and can take a little getting used to, especially if, like me, you have been running Gigabyte boards with the Award BIOS for a long time!