Currencies have network effects - everyone who will transact in a specific currency increase the value of that currency for everyone else. So one reason BTC is

Currencies have network effects - everyone who will transact in a specific currency increase the value of that currency for everyone else. So one reason BTC is worth more (speaking of entire market cap here) than, say, LTC, is because it is accepted more places. Another reason is that BTC is perceived (rightly or wrongly) as more stable than other crypto currencies. But all those legitimate reasons are amplified dramatically right now by speculation.