I'm leaning towards Coinbase as they have advised they will credit BTC with B2X after the fork.
I believe Bittrex will also do this.
ANnouncements are below:
https://support.coinbase.com/customer/portal/articles/2892985-segwit-2x-faq
https://support.bittrex.com/hc/en-us/articles/115002603211-Statement-on-Bitcoin-Segwit2x-hard-fork
Where are you keeping your BTC to ensure you get B2X??