From Hydrogenaudio Knowledgebase
QuickTime AAC is known to be one of the highest quality medium-bitrate CBR and VBR LC AAC encoders and is also another commercial AAC implementation. The current version of Quicktime supports Multichannel encoding up to 8 channels, and HE-AAC v1 with SBR.
Free Third-party CLI interfaces such as qAAC expose more modes such as TVBR (equivalent to quality modes in other encoders) and CVBR ("constrained VBR")
In recent tests for 64kbps HE-AAC and 96kbps LC-AAC Quicktime has consistently come out near the top. This also applies to higher bitrates such as 128kbps and is likely to apply to higher bitrates such as 160kbps and beyond.