tbear - 12:31 pm on Jan 10, 2013 (gmt 0)
I've read that 'the average person' has difficulty seeing the difference of images above 300 dpi.
Which seems to be a good resolution limit.
The format, as mentioned above, usually depends on the subject matter.
....which one is better and what are their differences?
Well, if you can't tell the difference (assuming your eyes are in good condition), then go with what you see yourself. If you discern no difference, then go with the smallest file size.