Is there any OS feature which is better in AmigaOS than in Linux or Unix?
Not really.
There are a couple of nice features, though. The way how AmigaOs (or rather Tripos) handles removable media is much simpler than it is on Linux. There, removable media detection and handling has to go through quite a stack of software layers, starting from udev up to the dbus-system and finally the desktop. Unix has no native concept of "removable devices" and hence has to go through hoops to get something like it (it is constructed as a server system, not as a user system, and you feel it). AmigaOs handles this quite nicely within the Os.
Also, directory access on Amiga can be transferred between physical devices. So for example,type in "list DF0:" on the shell, hold the output with ^S in the middle, then remove the disk, insert it into "DF1:" and continue listing from there. Do not try this with Linux or Windows.
The drawback is the complexity of implementing the required logic on the file-system basis. EXAMINE_NEXT (the corresponding command) is a horror for any author of a file handler, and it took years to get this done correctly in the Ram-Handler (or so I hope).
Also, the dos.library (aka Tripos) is (BPTRs apart) a nice "virtual file system" whereas on Linux, the file system is rather a subroutine call from a process perspective and isthere scheduled between processes, which requires an amount of overhead due to inter-process locking and communication. Writing *a simple* filing system on the Amiga is simpler as this type of process locking does not exist - there is a single process per file system. Unfortunately, it also means that writing a well-performing filing system is harder since it has to do all the threading itself. FFS does that, but is also notoriously hard to maintain.
Low-level primitives such as "message passing" are nice, but not quite on par with the requirements of today, namely isolation between processes. One would never do it this way today. It was simple, effective, but is also completely insecure.