I use the App for convenience because it's on the tablet and I can just pick it up whenever I'm passing. Plus it's constantly logged in. However there are times when it's a pain as there is no info about the posters, signatures and the like, and a long post (especially with quotes) just hides out of sight beneath the keyboard so you have to keep moving that to see what you've written.
Pros and cons - I still use the app though!
Rather than PMs, you have a greater chance of someone helping if it's on the website. Yes, it's an open public forum and open to everyone to see - but then whatever you discuss on here may well help a number of other people who are glancing in but not yet registered to post.