Alexa use to be a useless tool for measuring traffic, but maybe those days things have changed. There was a time (a few years ago) alexa toolbar was considered spam. Not sure if that is still the case. I try blocking the alexa bot in my robot file, but for some reason alexa still reports traffic findings. I'm sure that the numbers are skewed and despite my effort to block, alexa makes its best guess, but not sure how they come up with numbers if their bot is blocked. PR doesn't have the power it once did. But I still check out my PR at times. I use to have the google toolbar installed to do so, but now I don't bother installing. There use to be a time when webmasters would get riled up if their PR dropped, but today I don't think it has the same effect and those days of PR panic are basically over. I'll just say that it is better to have PR than not, but I would concentrate on other SEO functions and let PR take care of itself. Same with traffic -- concentrate on marketing and traffic will take care of itself.
I also prefer pagerank. As you get the higher pagerank, more people with trust your site ... then bring more traffic ... and increased alexa rank as well. In other way of thinking......If your website is interesting and has many resources (even its a new site with no pr), many people will come to your site and bring more traffic.... your alexa rank will increase ... Your visitor will refer to their friend to visit your site... make a review ... etc .... makes many natural links ... and then it will get your pr increased.. both is important to identify the quality website. its just like chicken and egg issue!!!! But, I prefer pagerank as its more accurate than alexa.
Having Top Serp is better and it will help you increase alexa rank and also get pagerank, if you get more backlinks.
Alexa is like a needle, and PR is like a battle axe. They can both do the job, but the needle is more accurate killing weapon. Alexa is more accurate rating of a website. But there's a point. Alexa is not accurate for sites with ranking of over 1,000,000. PR is accurate for sites with alexa of over 1,000,000.
Alexa is Dumb, if you have a site targeted at people outside of US and u get around a million users a month even then alexa will show you low rankings coz outside silicon valley no one knows who alexa is? More people have google toolbar than alexa so i will always go for google pr.
Pagerank is important when you are selling a link and alexa for your traffic. For me both are important.
Google PR is better..naah its best, because its earned by hard work done on those precious backlinks. while alexa rank is total B.S, as it can be easily manupulated.