OK, a little late reply, and I just noticed your question was posted before I announced the release of
PortablE...
If you want to compile stuff for 68k Amiga, then I would strongly recommend CreativE. It's almost identical to AmigaE, but with some improvements & bug fixes. Even so, the last official release of AmigaE itself is actually VERY good, so don't hesitate to use it either - it has almost no compiler bugs IMHO.
Although based on E, PowerD is not really E (e.g. operator precedence), and unfortunately it seems dead, so probably best to avoid it.
ECX is quite good if you want to compile PPC code for MorphOS, although some stuff (like OOP) still seems a little buggy. Don't bother with it for 68k yet, since that seems very buggy. In time it may get much better, so worth keeping an eye on.
Being somewhat biased (since I wrote it), I left the best till last ;-) . PortablE supports OS3/OS4/AROS/MorphOS, has lots of nice improvements over AmigaE & co, while staying reasonably compatible (esp. with the AmigaE compatibility mode).
PortablE is more of a "meta compiler" since it generates C++ *or* plain AmigaE code, which you must then compile. Due to it's high memory & processor usage, it is better used on a modern Amiga (say OS4 or AROS or WinUAE), although it might be OK on a highly specced 68k Amiga (say '060 with 128MB of RAM).