They both generate about the same amount of money, which equates to power these days, but the republicans are more in lock-step with one another than are the democrats. The democrats are a mixed lot of liberal, moderates, conservatives, etc. but the GOP are all either conservative or extreme conservatives. The right has a well oiled propaganda machine as well that preaches the same message of anger and fear to keep their base motivated. But society is shifting more and more to the left, states that were once solidly republican red are now going democrat. Virginia, Ohio, and Florida are all solidly purple and trending blue, and it's projected that Texas will be purple in 2016. So the future is bright if you're a democrat, but not so much for the republicans.
At the current time, the Democrats hold the Senate and the presidency, and thus hold 2/3 of the legislative power. The Supreme Court is more or less equally divided, tilting slightly to the right. Obama has appointed enough career diplomats and deputy assistants that both the State Department and many of the regulatory bodies are staffed by liberals, so I think it's fair to say that the Democrats have more power. But this is a moving target, and the gods of power generally don't favor one party for longer than 10 to 15 years.
Democrats are the party of the people, republicans are the party of corporations and the rich. Democrats are more inclusive, republicans are required to pass a purity test. As the demographics change it will strengthen the democrats grip on power.
The democrats. They work together and for the most part are on the same page. They have done a wonderful job catering to the poor, minorities an women while painting the GOP as bigots who despise anyone who isn't and old, rich, white, Christian and a male. Currently the GOP is disorganized, fighting amongst themselves. The GOP must rid their party of the progressives, liberals, RINO's and establishment republicans.