Both are good as an long term investments but altcoin market is too volatile and if you are a day trader or believe in short term profits then you can invest in ethereum and take advantage from each pump and dump which will give you timely profits and will also grow your bitcoins in short term.
I understand that both of these coins are good enough, but nevertheless I still prefer the etherium. In my opinion, using Bitcoin is a huge risk to my investment. But if all forecasts are implemented, then Bitcoin will become an opportunity for many to become very rich.