I am a proponent of debian, but to keep the playing field open...
Familiar is directly aimed at ARM, specifically on PDAs. It uses a debian-like package system, and has support by a medium size linux-on-pdas community. google "ipkg feed" to see what sorts of software is packaged for familiar.
Oh, no no no. Don't even MENTION ipkg in the same sentence as the Pandora.
Ipkg sucks. Period.
Familiar Linux isn't that good, either. I used it on my Jornada 720 before switching to 720degrees (straight Debian). I much prefer apt coupled with aptitude.
Last time I checked they weren't as seamless as .debs because no one has written a handy packager yet. Or have they?
Linux distributions
* dpkg, used originally by Debian and now by other systems, uses the .deb format and was the first to have a widely known dependency resolution tool (APT).
* ipkg , a dpkg-inspired, very lightweight system targeted at storage-constrained Linux systems such as embedded devices and handheld computers