It all depends on the load profile using the allocator. You never know, that said you cannot beat, in theory, a semantically specialized allocator for a specific load... in other words, the right way(TM). This means applications should bundle their own allocators for the various load types they have. The "generic" allocator is sort of an heresy for the lazy, short termists or those who are in hurry. Don't worry I still use such generic allocator, sometimes, but often I do mmap myself the memory and deal directly with it.
The system allocator is the one that comes with all the system's memory debugging tools and security (or lack of it), so you'd better not mind losing those if you want to ditch it.
