I am sticking with GDAX mainly because I feel safe on this exchange but I wonder if anyone else has used another exchange or moved coins from one exchange to another.
Arbitrage trading and choosing exchanges based on price at this point is probably not a good idea.
Bitcoin exchanges are notoriously unreliable and there's a lot to back this up. Bitfinex has been hacked before, Kraken has had complaints about an extremely slow and glitchy API with regular problems at peak times, and a variety of other exchanges have had problems or even vanished (Cryptsy).
There's also the fact that there may be exchange fees, transaction fees and volatility which would affect the funds. Including in the fiat system.