Sure, PC World's reviews can help tremendously, but sometimes it's nice to see a blow-by-blow comparison between the exact models you've narrowed down.

For that, head to . This handy site lets you compare two mobile phones or tablets side-by-side, giving you not only an overview of their features, but also explanations as to what those features' advantages are.

Let's use the aforementioned S3-vs.-4S as an example. When you type in the names of those two models and click Go, you'll immediately see images of the two phones side by side -- a great way to see just how much difference there is between 4.8-inch and 3.5-inch screens. (Answer: huge difference.)

Versus IO also tells you how many reasons there are in favor of one model over the other. For example, the Galaxy S3 has 19 points in its "Pro" column, versus just 10 for the iPhone.

Scroll down and you'll see those reasons spelled out in impressively plain English. Under the Connectivity section for the S3, the description notes that it has an HDMI output, versus "no" on the iPhone, and explains why you'd care: "Video and movies can be watched on a TV with HDMI input."