There are two reasons for this. The first is that in all likely hood three supreme court seats will opent up in the next 8 years, if not the next 4. My libetairian idology forces me to be a much stronger supporter of justices who tend to support a more conservative interpritation of the constitution, as opposed to those who would have a more liberal interpritation. Based on that I believe that Senator McCain will appoint far better justices than Senator Obama.
The second reason I want McCain to win is because of the current hot issue of universal health care. While I believe that every American should have access to health care, I am strongly opposed to the government being the vehical through which it is provided. With the current democratic attitude towards this issue it would be disastorous to have both a democratic controlled congress and a democratic president at the same time.
So while I won't be voting for Senator McCain or Senator Obama, there are 3 or 4 other candidates for President on the ballot after all, between the two of them I really do hope Senator McCain is able to walk away the victor come November.