If you talk about coins not from the top twenty, it is very difficult to find a good and promising coin now. Each person has his own opinion on this matter. But personally, I like the recently released project Aigo. They have an interesting idea, a good team, and therefore I think that their coin will have a great future.
I think the top twenty coins can be an option to be the hot altcoin because they have a big chance and have the potential to increase. But we need to realize that the other coin will have the same opportunity to increase. So if you can get more altcoin from below than top twenty and you already check the project, and you think that the project will have a chance to become a hot altcoin, then you can buy that coin but be careful, make sure you can buy at a low price.