My experience is very similar to Oakleaf's. I have a triple and use my smallest gears without shame on my hilliest rides. We have a lot of steep grades in southern Indiana and, even when the road isn't quite so steep, I still use my smallest gears with some frequency when my legs start to fatigue. It's especially helpful on multi-day tours. I've been told I'm a good climber (I've been on a quest to find my inner goat and am finally starting to make some progress) and I'm small, but I still need 'em. I also like having a tight cluster in the rear and being able to pick my choice of gear even on the flats. It's windy here a lot and incremental changes help me find a sweet spot no matter the terrain or weather.
I had some problems last year with dropping my chain going from my little ring to my middle ring. I got a new crank last year--a much nicer one--and haven't had that problem since. I don't know if it's the crank or just a better adjusted FD, but the shifting in front now is very good. Previously, I would hesitate to shift up out of my little ring, leading me to spin out . Now, I don't give shifting up as much thought. I run Campy on my bike for what that's worth.
It's so hard to know in advance what will work for you. It sounds like you've had good luck with your triple on your MTB. Climbing with a road bike will be different if, for no other reason, than the bike will be much lighter. If you're on the fence, I would suggest sticking with a triple. Better to have too many gears than too few.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher