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.
Some coins aren't in the Top 10 but they do worth more than some in the top. Horizen currently is undervalued despite the fact its tech is more interesting and promising than few in the top 10