Road Bike Gearing Ratios

What are the best gear ratios road bikes? And 24 / 27 or 30 speed bikes offer different capabilities?

I'm thinking buying a road bike. I currently use a mountain bike, but now have bikepaths pleasant to use. I'm not sure what to look for in a bike road. I want speed, but the ease of use (energy expended / output) is more important. Most of the roads and trails are relatively flat, but there are some Hils.

A typical road bike has two front plates, a tooth 39 to tooth 53. A typical rear cassette (gears game) is 12 to 23 teeth with eight out of ten gears. A road bike better than a 10-gear band back. The range can vary but a rule is as follows: 12, 13, 14, 15, 16, 17, 18, 19, 21, 23. Some guys run a 11-23 or 12-25, with 11 going for higher power (sprint) or 25 more laps (climbing). Today, any road bike range 8, 9 or 10 sprockets and two plates in front gives you the flexibility to tackle most terrain with ease.

single speed bicycle