In order to answer this question I need to get a bit technical and mention "gear inches".
This is number which represents how far a bike will move for a given turn of the pedals in a given gear. The calculation for derailleur bikes sounds technical but is actually fairly simple:
- The number of teeth on the front chainwheel divided by the number of the teeth on the cog at the rear, multiplied by the wheel diameter in inches (it can be done in metric if you prefer). It gets complicated with hub gears because you have to throw the hub gear ratio in there too.
For the sake of argument I'm going to use 27 inches as the wheel diameter for all the bikes as being on 700c wheels they'll all be close to this.
My calculations show that the Ridgeback (45 teeth divided by 18 teeth x 0.53 (lowest hub gear) x 27inches) gives you a lowest gear of 35.7 gear inches. This is low enough for most people and would get up most hills with some effort.
The lowest gear on the Cannondale (26 teeth divided by 30 teeth x 27 inches) gives a lowest gear of 23.4 gear inches. This is properly low and should be enough to get up practically any hill.
The lowest gear on the Boardman (34 teeth divided by 28 teeth x 27 inches) gives 32.8 gear inches. Lower than the Ridgeback but not as low as the Cannondale.
The top gears for the bikes are 109 gear inches for the Ridgeback, 108 gear inches for the Cannondale and 122 gear inches for the Boardman.
I hope this doesn't confuse too much and helps a bit.
Edit: If you want to do more comparisons,
Sheldon Brown's gear calculator is useful.
