I would say now, watching it rise, and since I've talked to bitcoin miners that say almost half the network is now mining BCC... well, it's looking like there is a real split and you should hold both ;-)
It's nice to almost double one's holdings, by sitting on the ass!
https://coinmarketcap.com/currencies/bitcoin-cash/
Some estimate BCC goes to $1500 by end of month; I can imagine just to wait and see at this point ;-)
I admit I was wrong. At this rate its more like end of the week. I didn't realize how many people wanted this. I still expect major crashing later but for now a lot of people are testing out both and its not so clear cut.