I've owned both 1900x1200 and the 1680x1050, the WUXGAon a D800 (main computer for over 2 years) the WSXGA on my current M70 (main computer since feb).
I really hated the 1900x1200. Font scaling in windows is not an exact science. Things are always the wrong size and I was always fidling with getting the text to a size I could read it in.
Also as my external monitor is a 19" 1280x1024 it gave me problems sometimes when sliding from one screen to the next. There is a 200 pixel verticle diference and the mouse would love "catching" on those 200 pixels.
OTOH I find 1680x1050 is perfect. Without messing around with settings/scalling the fonts are very readable. The 1050 is only 16 pixels off from my external monitors 1024 vertical resoltion, so no problem there and there is a final consideration. Games are going to look best in there native resolution. If you are playing games, the lower resolutions are going to be easy for your wussy laptop graphics to drive at the native res.
This is all very subjective. You need to go to a circuit city or CUSA and LOOK at the diferent reses. Decide for yourself