Make your own decision if you have to choose altcoins and do your own research, then check the ideas twice before you decide which one is good for long-term investment. But 3 years is a too big amount of time. You will need to check all market every few months and possibly rearrange your portfolio. If you need to invest and forget - get only BTC and ETH
Decisions would really vary on our own knowledge on where we do decide up things basing on what we discover or what we learn.If we do see altcoins that are suitable for long term then its our choice on what step we would make 2-3 year hold wont really be an easy thing specially if you are too active on checking prices because anytime you would really be tempted to sell out.