Well, from your description I'd take it you'd get the most mileage out of Five Nations, because you love Eberron and run 2 games with it. This sounds like a reasonable choice.
Iron Heroes is a very interesting choice, but if you have already trouble with interesting anyone for trying out Arcana Unearthed, Iron Heroes will probably meet the same fate. Arcana Evolved is a very nice book, but as it's mostly a compilation of older stuff, you don't really need it, even more so as you were not able to get any use out of AU. If you just want to update AU, you can use the
old errata and the document with all the
recent updates and errata for free
.
