I have a new monitor 27' that now has a Displayport as well as an HDMI.  My graphics card also has both, which one is the better hookup for the main monitor.

 

I have a 17' monitor that only has a D sub(vga) which I can use an adaptor for and run out of the DVI-I slot on the card.

I also run a 55"TV from HDMI out of the back of the card. I understand that HDMI is the only way to go if I want sound transferred to the TVs sound system with one connection.

 

This card GTX670 has a DVI-I,DVI-D ,display-port and another HDMI output.

If you aren't going above 1920x1080 then there is no need to worry about this issue at all. 

 

In the past, HDMI would not support resolutions like 2560x1440, so you either needed to use DisplayPort or DVI-D dual link. With the advent of HDMI 1.4, that distinction has mostly disappeared, but there are still some experts that believe that 1440p monitors aren't designed to work properly with HDMI 1.4. In order of my preference (assuming that you have the correct version of each cable to support 1440p):

 

DisplayPort--->DVI-D dual link-->HDMI.

 

DisplayPort does support audio transfer, but most A/V systems do not have a DisplayPort input. You can buy a DisplayPort to HDMI adapter, but then again, only the newest amps and receivers support resolutions above 1080p.

 

There are a few other minor differences between HDMI and DisplayPort, but none that would affect the use of any flight sim apps.