Thomas Richter's library is very well written and tries to do the least number of hacks and everything by the book. I have found it to be mostly bug free and as fast as the P5 version when configured for the fastest speed. It is also one of the most compatible and flexible when installed and configured correctly. However, it's by far the most difficult to install correctly. An mmu is required also.
What makes me not to install the MMULib version, is that it only works with a patched version of SetPatch from AOS 3.0/3.1 and i'm not sure if it's a good idea for AOS 3.9 users to do this. The latest version of SetPatch (44.48) applies a few extra stuff which improve stability.
Thomas is still supporting and willing to fix bugs despite his hardware being flaky.
He is? I thought that he completely gave up after his Amiga 4000 ceased to work. The recent Aminet release, contains a version that he had compiled in the past and forgot to upload it. I do hope you are right.