For questions about the system, either Meta is okay. We have plenty of people who have been using it for years.
For questions specifically about Ask Ubuntu (want to highlight a problem, ask us to do things differently, etc), here makes most sense but I'm sure there are occasions when Meta.SE makes sense too.
If you want to suggest a change to the underlying system (feature requests, reporting typos in badges or the help, etc), while SE staff do circulate around all the sites, you'll get a lot more feedback on Meta.SE.
Regarding badges and features on Meta sites, most sites have a cut-down feature-set. That is to say things available on the main site (reputation and various badges) are only available on the main site. Meta.SE is slightly different in that it is the main site. It has reputation alland all those gubbins.