There really isn't a best lens. There are so many options out there that you have to choose which is best for you and your needs. I will, however, steer you away from the kit lens. It's really not that good, it's not durable, and it's money that could be spent elsewhere. If you're ok with a lower quality lens like this at least get something like the 18-135. The image quality isn't spectacular, but at least you get a wide focal length range.
The next step up are lenses like the 17-55 2.8 and 15-85. Both are EF-S lenses, but regarded for good image quality. The 17-55 gives you shorter range, but a constant 2.8 aperture. On the other side, you get more range with the 15-85 but you don't get the wide(ish) f/2.8 , nor the constant aperture.
The problem with both of these lenses is that they put you into another price category (they MSRP around $800, but you could get them refurbished or used for less). For the same price you could get the 24-105 L. It's a kit lens for full frame cameras so a lot of people buy the kit then sell off the lens, brand new. You can get great deals ($600) on a really good lens. Much better build quality than the above, and good image quality. The downside is that 24mm isn't very wide on a crop sensor. But you could supplement with the 10-18 or 10-22 if you really wanted the wide side.
