I dunno, I'm actually a pretty big fan of mega houndoom in OU, great speed tier and power, plus it switches in for free on stuff like mega sableye and really punishes those fat bulky teams. In terms of typing, the dark and ghost resist is quite rare tbh and really nice to have. In comparison, I find mega gallade kind of lacklustre, it struggles with the common defensive mons in the tier and has pretty bad 4mss, lando-t and slowbro are so common and it only has 1 slot for either knock off or ice punch (even with knock off you're not beating mega bro anyway). Of course, sableye hard walls it no matter what too. That's just my opinion though, if every else is on board with mega gallade we can still go with that I guess.
On another note, do we have to keep this team discussion on this thread? I feel like doing this on skype or anything with an instant message/live chat kinda thing would be way better, it's difficult to get a proper teambuilding discussion going on a forum.