I create my Linode 512 just 3 days ago and I still have all my sites in my old VPS from other host. I was wondering if there's a way for me to test out which VPS is better?

I would suggest to ran a few test through apache's ab tool (install the apache-tools package). This benchmark (with others like siege) can test your webserver, and if you've got the exact same configuration (webserver, accelerators, php version and config, etc), you should be able to compare the results.