Originally Posted by
Dean V
12-25. You won't need the 11 for flat terrain and you get a 16t cog which is much more useful.
But you also don't need the 25, and an 11-23 gets you the 16.
Actually, no one can answer this question for the OP. It depends on a bunch of stuff, your intended use, how strong you are, your preferred cadence.
For example, if you don't race, and aren't riding somewhere with long steep descents, you don't need an 11.
But if you do race, and you prefer to sprint at a relatively low cadence (100 rpm or so), there will be times you'd want an 11, particularly for a downhill, down wind finish.
Conversely, if you're not a strong climber, even in relatively flat terrain you might want the 25 for the occassional bridge, or small hill, particularly if you're doing those into a steep headwind.