For FIAT x Crypto I'd go with KRAKEN , there was some time that it was overflow , but made the enhancements

For CRYPTO x CRYPTO I think BINANCE is the best option

Also there is cryptopia for small ALT's and one LTC market, if you are going to CRYPTO x CRYPTO I'd choose LTC whenever is possible as it[s fasta and cheap to transfer
but there is always something not so ok last time the NEO withdraw was off fot a few days