Personally speaking, a lot of my favourite routes involve anything up to and including 25 % sections of climbing ( not average gradients, those are exceptions on particular climbs). I find that a 34t - 28t will get me up most, without stalling and falling, on the 10 speed bike with the compact up front, and on the 9 speed bike, with the triple up front, I've personally rarely needed anything lower than 30t - 27t, if I'm load lugging. Gearing is a very personal choice though, trial and error will soon tell you what you require.