I was on Astrid too. I switched to Wunderlist mostly because their import from Astrid worked correctly. Wunderlist is OK, though I can't say I'm completely satisfied with it. Its UI is laggy (on a Nexus 4!) and unreliable, for example the auto-sync often destroys the last task I just typed in, or when I accidentally tap outside the task entry box the text I just typed is lost forever.

I'm looking at alternatives, and the one I like the most so far is Remember the Milk. Last time I tried it (probably a year ago) it was rubbish, but the latest version has a clean and fast native Android GUI and some nice extra functionality (e.g. geofencing). I'm thinking about switching, but it doesn't have import from Wunderlist, so I'll have to move about 200 tasks manually.