7-Zip has a terrible GUI, PeaZip actually I think did an excellent job on the GUI. It's all a matter of opinion in the end. A lot of "computer guys" prefer a techno or sharp look but I prefer a more soft and polished look.
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Definitely grab the 1.4 beta, it is organized better and has the one last feature I was missing from Task Manager - "switch to" (or "bring to front").
It's very stable too. Top notch software.
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It's good, in fact great... but the BEST and the king of Task Manager replacements is SystemExplorer. It's free, portable (I run it on my U3 flash drive), light weight, and gives access to much more than Process Explorer.