1. Democracy, we will be able to vote out party if we think they are not performing or they are corrupt rather than the commission being picked cause David Cameron wants so and so there and all the other heads of states
The European council only get to nominate candidates they deem suitable to sit on the European commission and the European parliament (the people YOU voted for) get to accept or reject them. If the parliament aren't happy with a candidate then they don't get in, its as simple as that.
So basically the heads of states (who have been voted in at general elections) nominate people which are then reviewed by parliament members (who have also been voted in by members of the public) and deem whether they are suitable for the commission or not.
What part do you actually take issue with? And what part of the process isn't democratic?