What is bad about either of these things? Really nothing that I can tell. For about the last year, I've been using the Sprint service and the Novatel U727 aircard on my Mac, both with OS X and Windows Vista, and it's been basically flawless. And thanks to a steady stream of software updates, it just continues to get better. For example, with the new Sprint SmartView download, you can now use the GPS features and see signal strength with OS X Leopard.
(I'm assuming) there are plenty of good reviews out there by Googling the Novatel card, so I won't waste my time.
Sprint has a really solid wireless network. Service is fast here in Portland, where I can download at about 200KB/sec. It's been the same where I've tested it in Seattle, San Diego, Sacramento, Fresno, Akron or Chicago. I even got connectivity last summer in rural western Montana, and the speed was just fine!
Lucky me... as an older customer I'm grandfathered in under the old "unlimited" plan, under which I'm not monetarily penalized for going over 5 GB of transfer in one month... but they could theoretically cancel my account or slow my access down to keep me at bay. I have never approached 5 GB in one month, and I use it pretty heavily, so I'm not worried.