SpeedNewer DSLRs at all levels start up and wake up almost instantaneously. For example, Nikon's $1,199 D7000 starts up in 0.13 seconds, just 0.01 seconds slower than the company's flagship pro DSLR.
The pro DSLRs do have faster drive rates and bigger buffers, so you can shoot more images in a single burst—important to action photographers, especially those who shoot RAW files. Canon's EOS-1D Mark IV can shoot up to 28 RAW 16-megapixel images at up to 10 fps, and Nikon's D3S can shoot up to 40 RAW 12.3-megapixel images at up to 9 fps—both with continuous autofocusing for each shot. Those are the speed champs among today's DSLRs.
But the lighter and much less costly mid-range models aren't far behind. Canon's EOS 7D can shoot up to 8 fps, while Nikon's D300S and Pentax's K-5 can shoot up to 7 fps with autofocusing. (The entry-level models aren't the best choices when speed is a prime need. Besides much slower maximum shooting rates, the entry-level models tend to have small buffers, meaning you can't shoot very many images in a burst. For example, if you shoot RAW images as most pros do, Canon's EOS T3i can shoot up to 6 shots at 3.7 fps.)
If you're not an action specialist or a photojournalist who relies on rapid-fire shooting, any current DSLR should be quick enough for your needs.
AF ConsiderationsToday's mid-level DSLRs offer excellent AF performance, and even most entry-level models can handle challenging moving subjects, so unless you specialize in sports or wildlife action photography, any of these cameras will meet your autofocusing needs. If you specialize in action work, the pro DSLRs provide better AF performance than lower-priced models from a given manufacturer. Even when they feature the same AF system, as is the case with the Nikon D3S and D300S, the pro camera's more powerful processor results in better AF performance. This is a vital concern for pro sports and bird photographers, less so for studio and landscape specialists.
Newer pro and mid-range DSLRs provide AF fine-tuning, which allows you to adjust the camera to compensate for consistent front- or back-focusing with a given lens. This is a feature many pros use, and it's not available on the entry-level DSLRs.
RuggednessPro models like Canon's EOS-1D Mark IV and EOS-1Ds Mark III, and Nikon's D3S and D3X are prized for their ability to stand up to tough shooting conditions. But today's mid-range DSLRs can handle a lot. Mid-level models like the Canon EOS 7D and Nikon D300S feature good dust and moisture resistance, and we once shot more than 400 images in a driving rainstorm with the cold-, dust- and weather-resistant Pentax K-5 with no ill effects. Just make sure the camera and lens are stated to be weather-resistant before trying that. (No DSLR is waterproof.)
The entry-level DSLRs aren't well suited for especially severe conditions, but can certainly handle "normal" conditions such as indoor and fair-weather outdoor use. If you don't shoot in rugged conditions, you don't need to pay for and lug around an all-out pro camera.