Well, yeah, all of the Action/Treasure cards that you buy are better to have in your hand than Copper or Estate, barring edge cases. Therefore, it is pretty much always better to get them early rather than late.
However, the cards where the difference is biggest are the cards you usually want to open with. Trashers are top of the list, and since Chapel is the best trasher in the game (other than Donate but you don't have to worry about shuffles there), it is the ultimate the-earlier-the-better card. Other than trashers, junkers and gainers also tend to be amazing in the opening. Drawing and economy are not AS important as you can add them later on and still be fine, as long as your deck remains balanced (i.e. don't over- or undertrash).
All this assumes that there is a reasonable engine you can play with. If not, then trashers and gainers are not so great. Junkers remain amazing almost regardless of the board, and Silver/Gold gainers can be added to the list in a BM or slog strategy.