BTC = gateway coin that you can trade for altcoins
XRP = i dont know why anyone would want this
ETH = the huge number of altcoins being ERC20 tokens should tell you that Ethereum is the best technology-wise but that doesn't mean it'll reach the highest price. there's no limit to eth tokens and the price will only go down as supply goes up.

ETH > BTC > XRP

However, BTC will _always_ cost more than ETH because BTC has a max supply.