My impression, from my own experience and a lot of anecdotal info from other Sprint subs (long time Howard Forums and Sprintusers member), is that Sprint's coverage in central and south FL is quite good, not quite as good as VZW's when you get out into alligator areas, but quite solid everywhere else. E.g., I recall roaming heavily on VZW on a drive from Cocoa to St. Cloud via FL 520 and 532, but got Sprint signal continuously thereafter all the way back to where we were staying in Orlando, and just about everywhere else I went in central FL on that trip (Clearwater/Redington, St. Pete, Tampa, Orlando, Space Coast). And I've been to SE FL before and remember the coverage down there (Palm, Broward, Dade, even Monroe, all the way down to Key West) to be quite good as well.
(I was surprised to see SO MANY COWS on that drive -- I never knew FL had so much ranching. But anyway. A good rule of thumb is that Sprint's coverage may not be so great if there are more cows than people where you are.)
OTOH, even when roaming I had no problem using my phone because Sprint roams just about everywhere it doesn't have native coverage. I've even been places where I got signal and VZW users didn't because Sprint allows extensive in-market roaming and VZW doesn't, and neither's coverage was very good where I was (it was a strong USCC area). The one downside is that you only get 1xRTT data (roughly EDGE speed) roaming on VZW (though you get EVDO on USCC).
As far as using the phone goes, you probably don't need anyone to tell you that the Android experience is a very different one from the experience of using an iPhone. It will require some adjustment, probably. But it's at least as capable and a lot more customizable. Battery life is not as good. But hey, batteries are cheap, I got two 1500 mAh batteries and a charger for like $30 from Amazon.
I'd say that since you're still within the trial period and you're not happy with your ATTM service, it certainly makes sense to try out another carrier, and based on what I know I'd be surprised if Sprint's coverage and QoS wasn't entirely satisfactory where you are.
What I'd do if I were you would be to keep the ATTM phones and also open up lines with Sprint. That way you'll have a couple weeks to use both handsets side by side, allowing you to directly compare their strengths and weakness. I always tell people to try out another carrier on a probationary sort of basis before switching or porting their old lines.
Good luck.