Right now I really only have one device, but we are thinking about getting a small flash based device for activities that would be too much for a HD based device. Given that it would be non-critical listening and space is a concern I would use CBR or VBR @ ~128kbps.
For my big device (currently 60GB) I use VBR High Fast (in MC terminology).
I would recommend trying LAME
-V 5 --vbr-new. It is already usually almost transparent with most music material. The average bitrate is normally about 130-135 kbps with pop/rock etc. Classical and other less intense genres can result a bit lower bitrates. Genres like Speed Metal may use more than 135 kbps.
If the quality is good enough then only one cache archive is needed for all portables.
Things may be different if you use an iPod with a dedicated headphone amp & high end cans in a quiet place for critical listening. Then perhaps a higher VBR quality level would be better.
Actually JRiver could add this setting to the VBR quality options and name it as "Portable". And perhaps also one setting below it for those who need to squeeze files even more.
The new options could be then:
Small Portable -V 6 --vbr-new
HQ Portable -V 5 --vbr-new
Normal -V 4 --vbr-new (= --preset fast medium, this is directly mapped inside LAME)
High -V 2 --vbr-new (= --preset fast standard, this is directly mapped inside LAME)
Extreme -V 0 --vbr-new (= --preset fast extreme, this is directly mapped inside LAME)
The Fast option (--vbr-new) is the currently recommended mode (by the LAME developers and
HA). The LAME developers have done a lot of work for making it as good or better than the old VBR mode. According to the recent test results they have succeeded. Currently the Fast mode is generally as good as the old mode and often better. Only a few minor problems have been reported.
The Fast switch could be removed and the --vbr-new mode could be the default mode. At least the now incorrect "much faster, but slightly lower quality" text should be removed.
Those who want to tweak LAME options can continue using the custom text box.