usb 3.0 card or a sata card to expand my server?

Well, just about out of room in my older lenovo pc that was repurposed and saved from dump and turned into a media server running WHS 2011. I do have some pci slots available to me, so was wondering what would be the better way to go? Currently have 3 media drives, and 1 OS drive. In a month or so will probably need a form of expansion to keep growing. Just wondering what would be better direction. I've been buying externals and cracking them open to add to my server to get to the 3 I currently have now. Just wondering if I should get a usb 3.0 card and start going that route to add drives or get a sata card and keep doing what I've been doing.I use Drive Pool if that makes a difference as to what advice you guys might give me. I was thinking the external usb 3.0 route would even make it better in terms of keeping heat down in my case(full size). Server is in a isolated room so sound and that type of stuff is a non factor. Welcome to all opinions.