I bought the 3G model of the first iPad, and have never regretted it.
There are many occasions in the field where I'll be served well by being able to reply to a mail quickly, or use some other services right where I am in the field instead of having to wait until I am in an office or working to tether the iPhone to the iPad.
That's just me, though. It's convenient for me, and affordable.
And this assumes that either AT&T or Verizon has coverage where you live, work and travel, and that it would be a real benefit to you and your workmates for you to be able to connect everywhere.
Don't believe any of the marketing hype about 3G, 4G, HSPA+ or anything else, though. Connectivity is damned slow. Resolution of certain Web pages is better now with iOS 4.3, but it's still going to be damned slow when you are only getting an average of, say, 1.5 megs when you're used to 25 megs at home and work.
For me, personally, it is very, very rare to be on an array that is faster than that, and that includes in the parking lot at the Pentagon, or anywhere else that you'd think we'd have the very fastest arrays and good backhaul.
It really *does* help your work to be connected, if you need that kind of connectivity. But it'll be slow.