Both card cost ~$70 What is your opinion which of them would be better to buy?

GeForce7300GT as default uses DDR2 memory, more faster than 6600, and has additional vertex shader block. So GeForce7300GT is more preferable. I recommend Gigabyte's one with passive cooling system silent pipe.

I have a Gigabyte 7300GT with passive cooling. It has 450/800 clocks and works fine. In most of tests my 7300GT works like 6600GT