If you are thinking of investing in altcoin, don't go without the top 10. I think investing in other is really risky. Those may end up in very short period of time. In can invest in lower market cap, if it has real usage/adoption only.
As this year has shown, investing in top coins is also accompanied by great risk. for this year, top coins as well as others have fallen dramatically in price. I would for the time being refrain from investing until the market is clear