Why bzr and launchpad? Bzr AND Launchpad are open source.
launchpad: open source
github: closed source
sourceforge: closed source (was open source in the past)
bitbucket: closed source
googlecode: closed source
You can submit changes to launchpad at: dev.launchpad.net. As well as (submit launchpad bugs) and feature requests against it if you don't want to make the patch yourself.
When there is a good open source alternative, I always choose the good open source option. I initially had problems with bzr a couple of years ago... but it has been quite good to me over the last couple of months. So I'm moving over all of my projects from other version control hosting services to launchpad.
Of course bzr and launchpad are also written in python (with selected optional C optimizations), so that makes for happy hacking :)
update: reported a bug here about the 'can not find source code easily on launchpad' issue. Any other issues with launchpad?