It is hard to predict whether or not Bitcoin will split. So, before the process of Bitcoin scaling is completed it is better to hold your bitcoins on a wallet you own the private key of. And here is the reason why.
In the "worst-case scenario" (for those who support Segwit2x) there will be several Bitcoins, like “148 Bitcoin”, “NewPoW Bitcoin”, “Bitcoin ABC,” as well as “Legacy Bitcoin”. If you own Bitcoin, that is private keys, you will automatically get the "new types of" Bitcoin.