Best to buy dollars and sell bitcoin peer to peer.

Next best is with a miner, though larger enterprises tend to work in scale that is impractical for working with individuals due to operational cost and risk.

Exchanges are filling a void, and charging fees for that while providing tools for order books, market making, price discovery, and past comparative value tracking. They are also incentivized to provide access to other products and services to make trade fees on.

This is similar to the difference between buying from a farmer vs the local supermarlet.