Most successful politicians are very charismatic people who generally make a great impression in person. However, that does not mean that they will actually advance your interests (unless you get to know them well enough to bribe them, most likely in an indirect way at this level). I would not worry so much about issues that affect a small part of the population (gay marriage, abortion, etc) since these are rather the "circus" in the "bread and circus" spectacle of politics. Economic policy is more important to our daily lives (but it is very similar for both parties despite the rhetoric); also foreign policy and monetary policy. In the last two aspects, the two parties are 99.9% identical. Like one party rule in China or Cuba.
For economic policy, the Republicans favor lower taxes (in theory), and individual economic freedom (again in theory). The Democrats' philosophy is more collectivist (we need to spread the wealth around for everyone's good and for social harmony). Who decides how that wealth is spread around (in return for votes or corporate pampering) is another story. However, we must keep in mind that one (the Republican) can lower taxes in name, but at the same time make us poorer. How? An easy way is by printing money - so they finance their populist agenda, but at the same time make the money we hold less valuable. This is a hidden type of tax. Another is by increasing import tariffs (imported products become more expensive, but it is not technically a "tax" if we aren't aware of it). Democrats do the same things, but aren't so loud about "cutting taxes".
I rambled long enough and I need to come to a conclusion. My sincere advice is to burn your registration in either party. It is tough if you live in Washington DC, but try to keep pure in this corrupt world. If, like me, you don't mind being a clown, you can support a third party (e.g., Libertarian Party, which advocates lower taxes, lower regulation, less centralization, focus on defense rather than imperialist expansion, and a stop to wasting our resources on victimless crimes and other such populist whims). However, despite my fondness for this party, I still realize they are total wankers. For this reason, I rarely vote (and when I do, it is in local elections, which matter a lot more to me, since they affect property taxes, the building of a walkway over a highway, etc - things that affect me in the short run).
Also, keep in mind that most political discussions are NOT based on logic, but rather on tribal sentiments and unleashed feelings. Politicians know that very well, and usually hire psychologists to help rally the masses behind various slogans. When you analyze it closer, they promote an "us versus them" mentality which gets people heated, and motivates them to go to the voting booth. Politicians, to be successful, cannot take the risk of following a principle and sticking to it.