Generally speaking, the higher the MP the better. You're taking the pictures at a higher resolution which means you can enlarge them to bigger prints if you wanted. If you never plan on enlarging anything past 5" x 7" the 6.3 will do fine.
3:2 refers to the ratio the picture is taken in. Prints are typically in this ratio- 2" x 3", 4" x 6", 5" x 7" etc. Digital cameras will usually always take pictures in different ratios than the standard 3:2, meaning some of the image will be lost when prints are made. The 3:2 is just a matter of convenience.
I've never found a difference of shutter lag on the same camera between resolution settings. I have seen it take longer to write the image and be ready to shoot again (of course this was back in the days of Compact Flash and Smart Media cards being the most prevalent memory cards), but with the advent of of SD and xD cards, that has been greatly improved. My 12.1MP Canon SD780 writes quick and I shoot at 12.1 all the time.
One big thing to reduce the blurriness in your pictures: Push the shoot button halfway down, let the camera focus, then push the rest of the way to take the shot. The autofocus is what I've seen cause the highest amount of lag between the pushing the button and the image appearing. A lot of people want to take pictures like they did with film (a single press) but digital doesn't work best that way.
Note: This is for point-and-shoot cameras. DSLRs are an entirely different animal.
EDIT: Also, agree with Blazerboy30.
