nextel...
I have used Nextel since about August of 1999. The reason I initially went with them was that they had a National Business Plan where there were no roaming or long distance charges anywhere you could get a Nextel signal (no one else had that kind of deal then - you were always wondering whether you were roaming, or not). That was the problem, of course. In 1999, Nextel's coverage was pretty much limited to major metropolitan areas (DC, here where I live in Madison, WI, Milwaukee, Chicago, Minneapolis, etc.).
Today, their coverage appears to be much better, with most cities of decent size (say...10,000 to 15,000 or more) having coverage, interstate highways having completely solid signals, even between hills, etc. Also, they seem to be pretty good about addressing signal gaps, as I have found a few when they start up coverage in a new area and then later find the gap filled.
Over the 4-plus years I've used them, I have had dropped call issues only once, but it was understandable. It was in Miami Beach when I was down there for a meeting during President's Day weekend, the Miami Boat Show (think: NBAA for boats) and the Coconut Grove Art Show. You couldn't get a room in all of the Miami area, much less get onto Miami Beach. What a circus.
One other thing I was told about dropped calls is that you have to make sure you stop in to a Nextel authorized dealer to get your phone software upgraded about twice a year. They do it for free and it takes about five minutes. Related to this, I have found their customer service to be decent, too.
I imagine your decision ultimately will come down to coverage areas. If you anticipate being in rural areas regularly, then get Verizon because it's unlikely that you'll get a consistent service in those areas from Nextel. I think Verizon uses tri-mode phones that include analog (the original cell signal), as well as digital. I would recommend Nextel if most (or all) of your calling will be from urban areas.
One last thing - although I don't use the Direct Connect (walkie-talkie thing) on Nextel much, it is nice and works FAR better than the Verizon deal, from what I understand. Nextel's entire system was designed with that feature integrated into it from the beginning, whereas Verizon, as I've read, has cobbled one together. I know a few people who have their whole family using Nextel (mom, dad, grown kids, etc.), because it's so much cheaper to use the DC deal - nationwide).
Hope this helped. Fly safe.