I hold 9 different coins. I buy the big ones (BTC, ETC, LTC) from Coinbase. I then send small amounts to various exchanges.
I use:
Poloniex
HitBTC
Bitfinex
The exchange you use depends on the coin you want to buy. Not all exchanges list all currencies.
For selling I normally use Local Bitcoins.
If you need any help, send me a PM.
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