I'm looking for a road bike that's primarily for commuting around town and pulling a trailer with two kids. It's been a few years since I rode so I'm a bit of a noob. Please give me reasons why one is better over the other, I'd prefer having easier upkeep as well.
One minor point: In the US you hardly ever find 5/10/15 speed bikes, except perhaps at WalMart. Generally there will be from seven to 10 cogs on the rear.
Re the "right" gearing, it depends on the terrain, but if it's at all hilly where you live and you'll be pulling a trailer, and you're not a gorilla, you need some low gearing to get the trailer up hills, so two or three front rings would be advised.
Maintenance is essentially identical for any derailleur-style bike. There's a little less maintenance if you have only one front ring, but the difference is negligible.
Mainly you want to buy a decent quality bike from a reputable bike shop, then take it back once or twice in the first few months (at least the first visit should be free) to have it tuned up (since shift and brake cables stretch when the bike is new). (You may be tempted to buy a fancy internal gear hub bike or some such. Don't. They're more expensive to buy and maintain, and generally less reliable. Re disk brakes, there are some arguments in favor of them, but no compelling reason for you to go with disks unless you like to spend money.)
Otherwise, wipe the chain with a rag and squirt a little chain oil (from the bike shop) on it every few months. (No need for this when it's new -- wait a few months.) Every year or two haul it back to the shop for a tuneup (or learn to do it yourself).
There are two main things to consider:
That is to say it matters not only how much gears the bike have, but how low and how high can they get.
As a suggestion, I would try a double compact or a triple chainring in front, with a rear cluster having the greatest cog around 28 teeth (for the hills), or 24 teeth minimum if you live in a flat area.
Hope this helps.
More gears != more gearing range. Are you in a hilly town or a flat one? Traffic-jamming or cruising longer distances between stops?
Close gears (i.e., many gears) are great for touring in flatter country because you'll be more likely to have just the right gear for the grade, the wind, the load, and your condition, and be able to stay in it long enough to matter.
In hillier country or when traffic-jamming, you won't stay in one gear long enough to care how close to just-right it is or isn't; having enough gears to cover the conditions you'll encounter will be more important.
I'll give some insight from my personal experience...
I was looking for something similar to you. I bought a 27 speed road bike that I currently use for commuting. I live in a flat location and I find that I only really use 2 gears, 1 for acceleration and small hills, and another for straightaways.
Keep in the back of your mind the route you will take to and from your start point and destination. If you are really using this bike for commuting you will probably have a prominent route that you take. If that is the case, it may be best to minimize the maintenance and possibilities of problems by going for a 5 speed.
Also, for easy upkeep, shy away from embedded gear boxes. Instead go for an external cassette, you'll be happier because you will be able to do the basic maintenance on your own.