AES ... is the sole most attacked cypher in history, and remains secure.
The 128-bit version remains secure. The 256 and 192-bit versions are believed secure but have shown cracks (they should really have had a couple more encryption rounds).
The 256/192-bit versions are just re-fiddlings of the 128-bit version, made to fulfill the NIST requirements for key sizes. This was largely a waste of time since 128-bits can't be brute-forced with any imaginable technology.
(My advice to any potential cryptograpy coders out there is to stick with the 128 bit version).