Firstly just to clarify, Ask Ubuntu is not strictly speaking "official", although it has had quite a bit of support from the community, and from Canonical. There is talk that at some point Ask Ubuntu could become official and replace the Launchpad Answers functionality.
In the meantime I'd suggest you use whichever you prefer, and feel you get better answers on. While you make up your mind which is most useful to you, doing as you've done here, and asking on both is perfectly acceptable in my opinion.
There are some fundamental differences in the format of each site though.
- Ask Ubuntu has a "voting design" with people competing to provide better answers, which can be voted up. There is a hope these can be useful and interesting to a wide number of people (or for more specialised questions easily findable through Google). Ask Ubuntu allows for a range of formatting (links, images, headings, bullet points, etc) not found on Launchpad Answers.
- Launchpad Answers is in a "forum style", essentially in the form of a discussion. This is particularly useful for troubleshooting problems because it allows for easier back and forth conversation. It is possible to ask a question about a particular package, and other people who are interested in that package will be notified by email.
As a very broad generalisation, I find questions on Launchpad Answers are hardware questions, whereas questions about software and the Ubuntu ecosphere tend to flourish on Ask Ubuntu.