Both are good, if you have already a mining RIG then it worth a lot because if you have reached the ROI then you are earning money like a boss now.

But even though there is a lack of motivation in the mining rig because people are saying that Ethereum is going to be moved to Proof of Stake which stops the mining and people will move to another coin.

Investing in bitcoin also is a good thing because the ethereum price has been increased too much recently, few months the price was ~$50 and now the price is $280