Which connection type for ati radeon 6870

If your monitor has HDMI, use HDMI, i think it's the most elegant method. But they are all the same in giving 1080p to your monitor, just different methods of doing so.

Great reply thanks, I read somewhere blu ray would have trouble playing across a VGA cable?

Possibly, i'm not sure.

I can't say i've tried.

In terms of connection priority i would do something like this: HDMI > DVI-I > DVI-D > DVI-A > VGA

So HDMI is top priority and it goes from there.