Originally Posted by ColonelSanders

The higher/bigger number of teeth on the cassette, plus the less/smaller the number of teeth on your crank.

So the Giant 3 & 2 have the same number of teeth on the crankset, 28/38/48, but on the cassette, the Giant 3's teeth go from 14 to 34, whereas the Giant 2's cassette goes from 11 to 32.

So for tackling hills you have the following ratio's :

Giant 3 - 0.8235 (28/34)
Giant 2 - 0.875 (28/32)

With the above, the lower the ratio number, the better for hill climbing. Admittedly the difference above is not that big.

The reverse applies to ratio's for gaining speed downhill or even on flat ground.

Giant 3 - 3.4285 (48/14)
Giant 2 - 4.3636 (48/11)

It is likely that you will encounter occasions where your speed downhill/flatish ground is limited by your gearing on the Giant 3(although you will still be going at a fast speed), but you probably won't encounter that on the Giant 2.