I've done my whole (large) collection in 192 kbps AACs. In addition to reasonable file sizes, the AAC format seems to work well with iDevices in terms of the effect of battery life. I'm absolutely not an audiophile, but there was another thread in which Trevor noted that I could drop down to 128 kbps and I wouldn't notice any difference while saving a little more space.
Personally, I prefer to have all my files in my preferred format. It means that I won't have to track down larger-size encodings if space ever becomes an issue, nor will I have additional considerations when it comes to other conversions I might do. I simply know that all my files are of one type and one encoding rate. Understandably, you may not see that as worthwhile.
When it comes to future compatibility, I don't see much reason to be concerned with AAC. It's not an Apple format, so I am confident that if iTunes or iDevices ever drops support for it, then there is likely to be something out there which I can use for conversion (XLD, Max, etc.).