The only member of this family with which I've had success here is Mexican Milkweed (A. curassavica) which is, more or less, perennial for me. Yes, it seeds here and there, but is easy to remove (I'm usually quite tender-hearted about removing them). In our recent mild winters, the plant has continued to bloom off and on. Some of these plants branch well naturally; others don't and are quite leggy. Pinching helps, but sometimes the branch and even the plant simply dies after pruning. They will be covered with nasty, yellow aphids, but these particular aphids haven't moved to any of my other plants so I leave them alone. Predators eat many of them. Some of the branching Mexican Milkweeds have been moved successfully; others died immediately. If you want Monarchs, you need to plant them. I find I don't mind the legginess given all the Monarchs I have year-round in my garden.
I really enjoyed your post. Thanks!
Since moving to Texas from the north, my husband and I have tried seeds of all the familiar northern milkweeds and we failed to get any started. But we did pick up a few Mexican milkweed plants at our local nursery and now we have Monarchs galore. Some migrate through our butterfly garden going north and others stick around 'til the new year. We've learned which nectar plants bloom all winter and we can show visitors all the stages of the Monarch's life.