It depends on what issue you are debating.
Politics are not simple enough to take down to "who...is making the US better?". You cannot take such a one dimensional view of the candidates (well I guess you could, but that would be a bit asinine). You should rather consider their views on each major issue and decide who you think is right there.
For example, I am conservative and therefore obviously support McCain. However I think Obama has a few social policies that are better than McCains. However I find McCain's economic plan and foriegn policy much more appealing than Obama's. Given this I support McCain, but that is not to say I think he is making the USA better in all areas, just more than the other choice.
