Of course "best" is totally subjective in the world of tea and in Chinese teas in particular cover an amazing range of flavors! From thick earthy umami funk of puehr, to black and oolong teas with distinct ripe-pineapple or muscat notes, and even ones with a hint of cool menthol. But I think the more extraordinary flavors are luck of the draw, maybe just the right happenstance of growing conditions and processing. I haven't particularly liked every pricey tea that I've tried, but the more extraordinary ones have tended to be not-cheap.
Most bagged tea, on the other hand, is a blend of commodity-grade teas, and the goal there is to provide a consistent flavor from batch to batch. So if I buy another box of PG Tips Gold a year from now, I can reasonably expect that it will taste very much the same as the one I just finished. Rather than whole leaves, you're more likely to find cut-tear-curl processed tea designed to release maximum flavor quickly. Whereas with loose leaf teas, you might get several steepings, and the first is not necessarily the best.