Probably doesn't matter for most divers, but the MK25 has a LP port on the very end, in addition to the 4 along the perimeter. I haven't ever seen anyone use it in either configuration, but pointing it downward is going to make it pretty inaccessible. Granted, you'd have to work pretty hard to find a use for a 5th LP port.
But, like everyone says, it is just a preference...low profile vs. running hoses. Just make sure you remember your preference. An instructor put my reg on my tank for me once, the other way...I was mighty confused when none of my hoses were in the right place.