Not an argument, I love riding my mountain bike it's ace, mint, cool awesome, sweet, sick, wicked, fresh, class, quality, sound, phat, dope solid, well good, safe, smoking, rad, boss and most high key!
I like riding my road bike but not nearly as much. This is because I hate cars seeing how close they can get without killing me.
In my mind I think mountain biking is harder, really long slow climbs, plugging through gloop but this morning trying to keep the road bike above 20mph for 6 miles nearly killed me and I've been out on the MTB every week over winter riding through some of the sh!test weather.
With the road bike it feels like every watt of power that comes out of your legs go straight to the back wheel. (this is a different thrill to singletrack but a good feeling non the less)
I think it has made me realise that as much as I'd pick up the MTB 1st time every time doing a few evening 10's has to be good training. I think 30mins-1hr fast on a road bike is worth a whole afternoon of mountain bike riding fitness wise. (not enjoyment)