Bitcoin is not the only, however the biggest cryptocurrency. The twenty others available have different properties, different from bitcoin.
Some twenty cryptocurrencies belong to the larger market, however none of these cryptocurrencies can be compared to bitcoin. The second biggest, litecoin, with its 10000 transactions per day cannot be compared to 70000 transactions of bitcoin system. The traded value of litecoin since December 2013 has often been greater than the traded value of bitcoin - 75 million dollars per day vs around 50 million dollars for bitcoin.
The essential difference between litecoin and bitcoin is the algorithm used when transactions must be confirmed.
The idea of cryptocurrencies is that everyone should contribute computing power and be rewarded, but the algorithm of bitcoin has proven to be carried out effectively by the powerful purpose-built circuits that outperforms all common computers.
The consequence is that a few large players today contributes with all the computing power in bitcoin system – sort of power concentration. Moreover, the massive calculations consume large amounts of energy.