ETH is much more popular and useful than ETC. But yes, you can invest a small part in it as a diversification strategy and hope for a bull run in future. But don't invest a big part of your income in it. It's just not worth it.
I also agree with investing more on ETH than ETC, because we see ETH greater trading volume than ETC. and certainly the future of ETH is better than ETC. but it's all up to him who wants o invest, because it is entirely his choice