what is the best butter substitute for vegan baking ( for a peach cobbler)

Coconut oil is considered one of the "good fats" and works well in most baking recipes.

I find Earth Balance to have a weird chemically aftertaste. I use coconut oil - refined if you don't want any coconut flavor, unrefined if you don't mind it.

Earth Balance “original”, they make baking sticks but the stuff in the tub is the same, just easier to measure with the sticks.

If you are working from an original recipe that uses butter, remember that it is only about 80-82% fat (the rest is basically water).
Margarine can be used 1:1 for butter.
If you use oil as a replacement, use 1/5 less of it than the butter amount in original recipe (e.g. 13 tbsp instead of 16 tbsp if recipe calls for one cup), and restore the water (3 tbsp in this example).

earth balance brand margarine bars; it is salty so decrease the amount of salt if the recipe calls for unsalted butter plus additional salt

Margarine or coconut oil. Both are full of saturated fat though, so not very good for you.