Story

I think they're both great programs but they're both flawed, too.

ArcGIS is better organized. The geoprocessing toolbox is well set up, and the search function makes it simple to find what you need quickly even if you don't know where it is. It has more users as well, so when you search for how to do something you're much more likely to find your question already answered. Its the industry standard so pretty much every GIS professional is going to know how to use it. Like I said though, it has its flaws. Its slow. It crashes and freezes way more frequently than any modern program should. This isn't just my install either, everyone I know who uses it feels the same way. Its like an old version of word. Save frequently or risk losing work. The license server bullshit is ridiculous. (I really can't stress enough how much of a pain in the ass that can be. For a program that costs as much as ArcGIS it should be flawless.) It is also absurdly expensive. The base package is expensive, and if you really want to have a fully functioning program you need to have a full license which is really absurdly expensive.

QGIS on the other hand is free, doesn't have that license server overhead, and I feel it is a bit snappier and more responsive than ArcGIS. It also doesn't crash or freeze anywhere near as often. ( I won't say never but I can't think of any time it has crashed on me.) Every new version comes closer and closer to matching ArcGIS in the number of things it can do and its ease of use. 2.2 really took a big leap forward, I think. (I'm still on 2.2, haven't switched to 2.4 yet.) It still isn't organized as well as it could be though. They've got all of the native tools under either raster or vector, which is nice, but they're aren't many native tools. The rest are under processing -> toolbox and then organized by which subprogram they're from (GRASS, SAGA, etc). It would be best if they just put everything under the raster or vector tabs and made which subprogram they're from transparent. That being said, as of 2.2 you no longer have to be able to work with GRASS' absolutely byzantine data model in order to use its tools which is awesome. Its really just how things are organized and documented at this point. If they continue to integrate everything and organize it a bit better they'll really have one hell of a program. I already prefer QGIS over ArcGIS for much of my work.

If you've already got ArcGIS bought and paid for they're is no reason not to run both. QGIS is free, so use it where it works better. If you haven't already paid for ArcGIS, hold off until there is something you're sure you need it to do that you can't do in QGIS. QGIS is really as ready for prime time as ArcGIS at this point and a hell of a lot cheaper to run and setup.

Cheers,
-WW

As a side note, I can login, and I have, but it doesn't seem to recognize that I've logged in on most of the site, which is a pain. I don't know why.