To figure out which service might give you the best coverage, there's 2 things you can do: as already suggested, have several people come over with their phones and see how good their signal is; second, look online to find out what towers are in your area - the closer the carrier's tower, usually the better the signal (unless of course you live in a geographic location that interferes with signal reception). Try sites like http://www.cellreception.com/towers/ and http://www.antennasearch.com/
And I've been told that prepaid phones thru the major companies (like ATT, Verizon, etc) do have different reception than their contact plans. Why/how, I don't know, but that's what I've been told multiple times, and sometimes I can't tell a difference btwn mine and someone who is on a paid plan, other times I can't get a signal yet someone that has a paid plan will (both going thru same towers).
Re cell phones - yes different cell phones can different reception. I've found the best way to find info on this, is to read reviews about a specific cell phone model. Reviewers will often mention how good/bad their reception is. LG seems to do pretty good (what I currently own), and several Motorolla and Samsung phones have great reviews when it comes to reception and call clarity.
Service Plans. First, figure out which towers are close to you, and try to get a prepaid service that uses that provider if you can. Once you know this, then you'll be better prepared to look at providers (there's no point in looking into a provider that uses Sprint for instance, if there's no service in that area!)
I've used Virgin Mobile for years (they use Sprints network), simply because they don't charge that ridiculous (IMHO) daily access fee. They offer a few different plans, such as a per minute plan (mine is 18 cents/min, but that has been carried over since I first signed up, I'm pretty sure its higher now, 20/min I think) or monthly plans ($20 for 200mins). I'm also not a heavy phone user, and use mine for phone calls and occassional texting, and usually spend about $15/month. You have to add time every few months, $20 every 90 days OR $10 every 45 days - although there is one of those cards that gets you access for the year (I think its $100). They have very basic phones up to those that have keyboards, MP3 built in, etc.
My mother recently switched from Virgin to Tracfone. Their rates are probably about a cheap as you can go - it varies somewhat, as the more you spend, the more minutes you get. The best thing to do however, is get one of their phones that comes with double minutes for life - that way every time you buy time on your phone, it is doubled (spend $20 for 60 minutes, and you actually get 120). If you don't get a phone that comes with the double minutes for life, you can buy it for $20, but why do that when you can get it included with the phone (just ck the packaging, it will say). With this service you also have to add money/minutes every 90 days unless you get one of their cards that gives you service/minutes for a year ($100, year of service, 400 minutes). Most of their phones are pretty basic but still very nice. As far as carriers, it depends on your area and the phone - tracfone will tell you which ones will work for your area, probably based on what cell phone towers are nearest you. My mother's goes through Verizon's network towers I believe. While Tracfone doesn't always have the best reviews online because of their customer service, frankly in all the years I've been using a cell phone I've only ever had to contact a customer service person once, so this wasn't a big consideration for us. In fact since I've been needing to use my cell phone more at work, I'm considering switching to Tracfone as well.
Another one you could check out too is Net10, owned by the same corp. that owns Tracfone. Their prices are 10cents/min all the time, regardless, so in that regard very simple plan. They also carry some nicer phones for those into that.
Hope that helps, and good luck!