Hello,
I plan on building a rover (like this one) but I need some advice on motors.
I want the rover to be fast but also powerful.
Not looking to get blazing speeds or anything, but I want to achieve decent speeds.
Please keep in mind everything will be powered off of a battery, so the motors shouldn't use a lot of power.
Thanks in advance.
No idea what you consider a decent speed or a lot of power, and that link doesn't take me to a product, but perhaps you could look at RC models of a similar weight and see what sort of power they need to get the sort of performance you're looking for. There are some fairly common motor/battery combinations and it's just a matter of choosing one that meets your performance/duration/cost/size requirements.
The webpage I linked contains an article about an Arduino rover.
I know my initial post was a bit vague specification-wise, but I don't really have any specific requirements.
Just want the rover to work properly and not be too slow 
artaex:
work properly
too slow
Unless you can define these terms, they are meaningless. You need to have some quantifiable requirements for performance, otherwise it's pointless discussing what you need to achieve them.
When I open the URL you provided I am taken to http://www.robotshop.com/blog/en/, which does not contain any articles about rovers.