What type and brand?

I searched for transmission fluid changes and found that a flush is not recommended. I'm going to stay with regular DexIII and not synthetic. My question is, should I stay with GM or go with a different brand? I don't know if all DexIII fluids are the same from brand to brand.

On a side note....is there a better transmission to replace a 4L60e that is a direct bolt up that doesn't require chassis modifications or anything like that?

I ran the valvoline max life dex/merc with no problems in my stock trans and built trans