The competition is really between the ASRock N68C-GS FX AM3+ and the GIGABYTE GA-78LMT-S2 AM3+, I would not recommend the ECS or the BIOSTAR since they are socket AM3, which only supports Phenom IIs, Athlon IIs, and some Semprons. If you are planning to use an AMD AM3+ CPU (such as the FX 4100, 6100, 8150, etc.) then you must choose between the ASRock and the GIGABYTE boards. If you are using an Phenom II, Athlon II, or any other AM3 CPU and really love either BIOSTAR or ECS, then I guess you could go with one of those.
Other than that there are not many differences, the only differences I see is RAID configs supported, the ASRock supports Raid 5 while the Gigabyte does not. The other difference is USB IO connector count, the ASRock board has 2 USB I/O connectors compared to the Gigabyte board
Why do you say that? While I know Gigabyte is a reliable motherboard company, ASRock is too.
Oh and another difference: RAM support:
The ASRock Support DDR3 800/1066/1333/1600
by default but is limited to only 8GB max
while the Gigabyte only supports DDR3 1066 natively with 1333 support if you OC
but has double the max memory (16GB)