every coin's worth is based on btc
PPC/BTC
ZTC/BTC
etc
The current top is IFC, you earn 7 times more mining IFC than BTC, or you could also say that you mine 7 times faster than mining BTC.
Just go to the alt section, use the search button and so on. Mining BTC with low hashrate is not worth it, thus we have so many people mining alts.
The price of alt coins doesn't go down with the rising difficulty, it goes down when BTC gains more value in USD, and if you use common logic that means that they just adjusted to their value in USD.
http://coinmarketcap.com/