now that you got things explained easily, lets screw things up

neither of those really affect picture quality...

of course bigger dpi is always better (so N900 is superior to N8) but those colour depth specs are purely theoretical values announced by screen manufacturer. when those are measured at every single point of the screen, they are starting to matter.
is the colour same at every part of the screen?
is the backlight even?
what about viewing angle? does it change for example contrast at different parts of the screen?
are the colours properly calbrated? does r,g or b get saturated too early?
what about display chips ability to output the best possible image (dithering for example)?

but OP wont probably even see the difference and N900's screen is probably better quality than N8's in the first place when looking at device price, even when N8's screen is probably year newer.

and resistive vs capacitive shouldn't affect much and the effect is even which makes the difference probably impossible to notice..