I very much like the ergonomics of the D70 over either of the Digital Rebels, but I'd probably go with one of the Canons, because of the glass. The absolute top-of-the-line Canon and Nikon glass is going to be very similar, but I believe that Canon has a significant edge in the middle of the price range (I'd consider this to be $300 to $1000). Specifically, the vast majority of equipment used on this site seems to be a medium to long telephoto zoom. The 70-200 f/4L (plus maybe the 1.4X teleconverter) is an absolutely fantastic lens, and is unmatched my anything in the AF
-Nikkor line, in terms of the combination of features, quality, and price. In fact, this lens basically lives on my camera now, as I don't think I've used anything else to take aviation pics since I bought it. Ultimately, you'll probably upgrade your camera body if you get one of the Digital Rebels, as they don't have the features of Canon's semi-pro line, but its really the glass, and the photographer that make the picture what it is.