Interesting question, but hard to give a complete and short answer. I am very interested in politics, but struggle to find any party that I would agree with on more than a couple of subjects. I wouldn't be able to speak in terms of US parties since I am not very familiar with US spectrum, but on the french spectrum, I am most definetly on the left side, but disagree on many issues with all the left side parties (just less than I disagree with the right side)
Being a scientist at heart, I tend to believe in scientific progress as a high priority, since it could help us solve many issues. Thus I am in favor of free high quality public education, and public research funding.
I also believe that to ensure that we can really get the best from the population, income redistribution is a must since otherwise, a lot of potentiel is wasted. I reject capitalism as I find it so inefficient as a whole (no sharing of information, etc).
Of course, that means I am willing to pay for it, thus I am in favour of high taxes for high income (I even think that a maximum income should be considered at some point)
I also tend to think that we should favour things that benefit the society's development as a whole, planning long-terms infrastructures and projects for example.
This is where I get most of my differences with the left-wing in France : I believe that we should invest in nuclear power at least until we figure out wether fusion reactor are doable/worth it. I also believe that GMO should be investigated, because potentially it could be a major breakthrough for mankind. I do not outright reject transhumanism either, hence why greens are not exactly my friends
Most of the time, I end up voting for one of the left-wing parties, usually the PCF (french communist party) because they are the ones that are the less nonsensical IMO. Often I find them to be right for the wrong reasons though