"Are you going to race? Or just ride a bike on road that happens to have thin tyres and funny bars? If the latter just use the same pedals you have on your MTB to save hassle. "
hmmmm, i rode a bike on road that happened to have thin tyres and funny bars for over 25 years before i even thought about entering a race because oddly lots of my rides tend to be longer than any race i've done, in both ride and race instances road pedals have a more secure fit and offer more support than MTB pedals.
Shimano, Look and Time all feel pretty much the same on the bike with subtle differences in clipping in/out and float, Shimanos and Times just work, although you can't put Shimano pedals on a bike with Campag on as it's 'wrong', and Look cleats wear out in 3 days.
i haven't tried Crank Brothers although i hear they have great warranty.