When it comes to exchanging Bitcoin people are looking for the reliable exchanges with low fees of course. Besides these two factor the key factor of the good exchange is the exchange that have daily volume above the thousand of Bitcoin. The best exchanges with above mentioned characteristics (low fees and high daily volume) are: BitStamp, Poloniex, Coinbase, GDAX.
The best question is what you consider as a large quantity of money. Maybe the best choice for you is OTC exchanges (OTC - over the counter). OTC exchanges refer to companies or individuals to sell you Bitcoin directly and not through a regulated and automated platform.Here are some characteristics of good OTC exchange and its benefits
High liquidity- OTC companies are specialized in supplying high volumes of Bitcoin for the buyers that are buying large amount of Bitcoin, for example institutional investors. Using this companies for buying Bitcoin means that you will be able to get your order faster than through traditional exchanges.
Fixer price - with the traditional exchanges the price is not fixed and the reason is that you are finished buying Bitcoin from cheap sellers, you gradually move to the expensive sellers. The price is rising as your order is being executed. The opposite is with the OTC, when you are buying Bitcoin through the OTC companies you can negotiate a fixed price and this is a pretty good benefit. Some of the most popular OTC exchanges are: Genesis, ItBit (mainly for companies), Richfund, etc.
Buying or selling larger amount of Bitcoin can disturb the market and drive the price up or down. If you want to avoid this, the best advice is to use multiple regular exchanges and buy a smaller amount for example up to 50 Bitcoins.