I've used a few different kinds with my kids.
Similac, Enfamil (regular and fussy) and Target.
Powder is defintely cheaper overall than ready to feeds, especially when they start taking several ounces at a time.
But I've used both - at the same time - when a ready to feed was low, I'd add water and a scoop of powder, etc... I've also supplemented breast milk with formula in the same bottle. Really, whatever your little one will tolerate is just fine.
If you're looking at formula, start with low cost stuff first. $12 for a can of Target's brand hurts a lot less than $34 for a can of Enfamil! And the ingredients are identical, it's federally regulated. It's just the texture that's a bit different.