My question is if it's still worth buying Asic's and start mining BTC in 2018.
If not mine BTC what other coin is it worth to mine nowadays?
Mining of bitcoin are still profitable, but this may change at any time. The price of bitcoin often changes, so many people do not want to take a lot of risk and buy expensive equipment, which later may be useless. Although on the other hand, many people have long predicted the death of Bitcoin, but he holds the bar high and now shows good stability.
Yes, you are right. bitcoin is very profitable if at the right time. because bitcoin is always up and down. I think bitcoin will always go on, because more and more people are using it, and that really affects bitcoin