Nvidia based mobo...should card match chipset for better compatibility??

suggestions?? i use my system for all different things from general
use to gaming to digital photo editing.

i use a giga-byte motherboard based on the Nvidia chipset...should i
consider switching to an Nvidia based video card for better
compatibility or does it really matter?? i currently use an ATI card.

if i switch to Nvidia based...what brand? i have used PNY in the
past...i liked the card a lot.

considering:

PNY Verto 6800 GT 256MB (what does the GT stand for??)

or

PNY Verto 6800 128MB??

suggestions??

thanks in advance!
tw