Yes adaptive relax should be the default, its what i used 99% of the time. The only time i dont want adaptive is when i need to use unwrap relax with pinning points. Adaptive relax should be the first thing you do to your uvs after selecting edges and hitting unwrap. I usually do it a couple times with a strength of about 250.
Note that although adaptive UV is excellent most of the time - I personally find isn't 100% accurate with fully spread uv's (for example a spread cube like in the image above.
In which case I use unwrap relax, which gives me straight lines and therefore more crisp normalmaps, etc ...
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It's near the bottom do a search for "UVRatio.py" you want to download sample196_v2.lzh it's in there.
There are a bunch of other useful scripts there as well, though it's all in Japanese and Google translate doesn't help much.
Hmm weird, never had that problem... always works flawlessly for me.
Well I just read in the Modo forum that you have to relax the uv's adaptively rather than default to get the exact same ratio. Here. http://forums.luxology.com/discussion/topic.aspx?id=20655&show=space%20scale%20uv
In which case I use unwrap relax, which gives me straight lines and therefore more crisp normalmaps, etc ...