I've had great luck with both brands. (semi-modern) Moved from a 4200Ti to 2x 8800GT SLI to a 5870 to 2x 6950's (one ended up being moved to my "steambox"), and just pulled the trigger on a shiny GTX 970. Go where the value is. Both sides work just fine right now driver wise.
Current setup: desktop: GTX 970, steambox: radeon 6950, laptop: 650M.