Honestly, I don't even try to have "one exchange platform to buy everything". I got Bitstamp for the big players (BTC/LTC/ETH), Binance for a few Altcoins (it's really good for this), and Bitgrail for XRB (that I couldn't find in a lot of places at the time).
I also used to buy on coinfloor but the instant purchase fees were so big I had to change