If you took a series of photos with each one of the cameras and printed them all to an 8x10 size I doubt if one would be any better in image quality than the other and you probably could not tell the difference except for certain characteristics once you learn what they are from each camera.
There may be some differences in color but what you like is a matter of preference.
That said I would give the most serious consideration to the Canon Xsi. Better specs than the Xti I do like the menu system of Canon best (very much like your G7) so if you like operating that you are a step ahead. Based on specifications I think the Canon is best.
What it is missing is a swiveling LCD like what they have on the S5. Nobody seems to have this feature on a DSLR and I do not know why.
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Currently I have a Canon G7 and a Lumix FZ18. I have been thinking about upgrading my camera to a DSLR (will be the first one). I have a small hand, and a Canon 40D, Nikon D200, or Pentax K10D sizes is just too big for my hand. I like the feels of entry level DSLRs, especially the Olympus E-410. Now that the XTi (400D) is replaced with XSi (450D), D40x with D60, and E-410 with E-420; what is the best picture quality among the above three? They are all about the same size, with XSi is the biggest in size. I am not planning to buy more than one type of lens, and will use the camera for general purpose (no fast or sport actions - mostly still photography). Thinking of having just the standard zoom lens which come with the camera (35 mm equivalent of 30-120 mm?). The plus about the E-420 is its small size (I believe it is the smallest). The minuses are the 4/3 which has smaller sensor than the other two, and it does not use SD card. Could someone comments? If you have to buy the lens separately (not as a kit), what specific zoom lens among the three that will produce the sharpest photos? Finally, the reason of switching to DSLR is because of sensor size and noises in P&S. I notice that E-420 with 4/3 system actually has approx. 30% less sensor size (area) than the other two (APS-C size). Does this make a lot of difference in terms of getting less noise pictures at higher ISOs? Thanks for info.