Changing the large chainring by 1 tooth is a smaller percentage change of ratio than changing the small rear sprocket by 1 tooth.
Bigger chainring and sprocket = smoother action, less friction, and less wear.
Smaller chainring and sprocket = marginally less weight and marginally less aerodynamic drag. Negligible effect for everyday riding.
Other considerations are simply what is readily available, and what looks better to you.
The gear inches thing is often a useful comparison because a simple comparison of ratios assumes that the two bikes being compared have the same wheel size.
You can of course look it up on a gear calculator online, but I think it is always nice to understand what is happening and to be able to work it out yourself. The calculation is easy enough:
- Take the number of teeth on the chain ring.
- Divide by the number of teeth on the sprocket.
- Multiply by the diameter of the driven wheel in inches.
Example: 49/17 x 28 = 80.7 inches.
This means that the gear ratio produces the same effect as if you were pedalling a directly driven wheel (penny farthing or unicycle) with an 80.7" wheel.
Technically, you should also factor in the length of your cranks, but as most modern bicyclists use cranks of 170mm +/- about 5mm, the effect is negligible. In the world of unicycling, we use cranks from around 75 mm up to about 170 mm and then it really matters.