The forex of cryptocurrencies, bitcoin as the base.
DASH vs Bitcoin
DASH is a privacy-centric cryptocurrency focused on fast and private payments - an alternative of digital cash. It is built on Bitcoin, solving the problem of its pseudo-privacy and traceability of Bitcoin transactions.
XMR vs DASH
Generally speaking the privacy features of Monero are better than those of DASH - read here.
There is a controversy about DASH since the developers mined 2 mil coins right after the coin’s inception. There is currently about 7 mil DASH which makes its creators potentially powerful whales.
Last update 01 Feb 2017: They say you need bitcoin to get altcoins but the fiat to alt markets are slowly appearing on previously bitcoin-only exchanges. For the gambling trading you need the liquidity of Alt/BTC pairs though.