It really depends what you want to get out of them, and how they are built up leg wise. BA is one of the easier ones (together with AA depending on you flying) to get status on - but it requires 4 BA metal legs per year (which is difficult if you never go to Europe).

Also what kind of money would you be willing to spend to keep DM. There are fares ex-Europe that would get you the necessary points for about 20000 hkd timed correctly. I flew OSL-LHR-HKG-SYD return for 21000 hkd a few months ago... (I think that was close to 400 points according to the new chart).