I think a link would be faster. In both, the web server will be going to the link specified by href. However, a link would just be that - a call to redirect. However, a button, as far as I am aware, sends much more data to the webserver, and also has many more things react to it - aka more overhead. Therefore, the link may be faster. However, it would only have a marginal effect really, unless you had a lot of traffic to your website, so I don't think it matter to much - you should probably just go with whatever you feel comfortable with.
I also just wanted to point out that I don't think using javascript to navigate to the page like that may be the best idea, regardless of whether you are using links or buttons. Serving webpages is a job for the webserver, and thus javascript calls may not be the best. Using the language that you are using for your web server (and if you are not, then I suggest you start using a back-end for your website), you should be able to respond easily to the button click / page redirect. The upside of this would be that it would also allow for any extra work to be done on the page as required.