34-25's been fine on my roadbike so far. I got another 11-25 on wiggle since I needed to add some money on there to use their current batch of coupons. If I didn't have a compact crank I'd probably have gone for the 28.
On my commuter/tourer I got what I believe are 12-34 on the rear and 46-36-26 cranks to match. 40lb bike with 30lbs of equipment going up a steep incline w/ 10mph headwinds and I was still able to keep pedaling, though it was still just as miserable as it sounds.