Yes at first approximation they are the same, but the mechanism of the update is different since one can be a delta and self-applied update and the other installs a complete build rather than patching the OS.
Digging deeper, the OTA update implies the OS and device is working properly, so iTunes is a good bet if you really want to ensure the update goes well or want to put the device into recovery mode to ensure the new OS and only the new OS is written. Obviously, if the device is having problems, you may opt for iTunes to control the update rather than hoping the device installs the patch properly.
Assuming your device is working well, you can safely update OTA and in many cases - the download is a delta update that is smaller than the entire image if you are doing an update that isn't a major version (4.0 or 5.0 which started the OTA capabilities and presumably 6.0 when it ships).
Using iTunes also gives you a chance to transfer purchases and reduce the number of apps you will have to re-download after a major update. Again, not an issue on incremental updates like 5.1.1 update from 5.1.