As far as with "professional" photographers using SLR, we actually use both SLR and DSLR. SLR's tend to have more variety as far as with medium format, small format (which are most DSLR's) and large format. Not to include the film, which comes in large large varieties. Ultimately, your purchase is going to have to come from what are you most comfortable with. Canons are great cameras, and so are nikons (especially since I use a Nikon for all my work), it ultimately depends on you and what your comfortable with and how well you know the camera on Manual mode. Unfortunately, a lot of stock sites, especially Iphoto and Getty, don't like pictures that use the built in flash. If your new to photography, you should look at a lot of techniques and how to to gain a better understanding of what makes a photo and what makes a snapshot.
