Jo-pa, open your own thread if you have a question. The poor OP can't even get an answer before you start hijacking his thread.
To answer the OP's question...
The short answer is that there really is no difference in practice in most cases.
The longer answer is that DisplayPort is a more modern and more capable standard than HDMI. DisplayPort supports higher resolutions, higher bit depths, and in some cases multiple monitors through 1 connection. Display port outputs tend to be more versatile because they can be converted to pretty much any other format via fairly cheap cables or adapters. The opposite is not always as easy. Having said that, HDMI is very capable and it's safe to assume that HDMI meets or exceeds the capabilities of the monitor (otherwise, it would come with a different input option, right?). Therefore, it is nice to have DisplayPort on the output device for better versatility and future proofing. On the input device, digital DVI, HDMI, and DP are all fine since they will be matched to the capability of the monitor anyway. Incompatibilities are possible, but they usually happen with older monitors that have analog DVI inputs or were based on early (probably not well proven at the time) DVI/HDMI standards.