I would think it is a little unusual for either to fail before 100k. I know there have been examples of manuals and automatics failing at ridiculously low mileage, but I think that is the exception rather than the rule. Following the recommended maintenance schedule will ensure anything but a defective item last the test of time.
If you are only looking for 100k then go with whatever makes the most sense for your driving needs. Sit in bumper-to-bumper traffic for an hour every day? Get an automatic. Drive in town all day with a 35 mph speed limit? Get an automatic. Have a lot of open highway miles ahead of you? Pick up a manual. Like to run on the twisty back roads at (or above) the posted speeds? Pick up a manual.