There are so many factors involved that I don't think there can be one definitive answer.
That said, and with the understanding that we here in the US have still not adopted the ISO216 paper standard (so I'm doing my calculations American style and converting....)
If you're using any printer OTHER than an Epson:
Good resolution is 1245x1755 (8.3x11.7 inches @ 150 dpi)
Better resolution is 1660x2340 (200 dpi)
Best Resolution is 2490x3510 (300 dpi)
If you're printing on an Epson:
Good res is 1494x2106 (180 dpi)
Better res is 1992x 2808 (240 dpi)
Best res is 2988x4212 (360 dpi)
But if you're using an Epson, I wouldn't in reality go above 240 dpi. It takes a well-trained eye to distinguish between 240 and 300 dpi images.
The reason for the difference between Epson and non-Epson is that for most printers, the printer's native resolution is at or about 300 dpi. For Epson, the native resolution is closer to 360 dpi. Native resolution is define as that resolution where sharpening halos are passed through the printer without being either enlarged or reduced.
If you're not going to use the printer's full native resolution, then you tend to get better results by using a resolution that is a harmonic of the native resolution. In both instances, you will note that the 'good' resolution is 50% of the native resolution, and the 'better' resolution is 66.66% of the native resolution.
I must admit though, that the dimension could be off due to conversion. How you people manage to measure paper in mm, resolution in dpi, and keep everything straight is beyond me.
- joe U.