I would say 1. Simply because the split in the trunk will facilitate your ability to cut and grow from the stump while the uncut one provides the photosynthetic resources to facilitate quick grobat before you cut the sacrifice off, you could air layer it. Two trees for the digging of one. Let us know what you choose. In my opinion, without a doubt 1.
If you can take 2, get 6 as well. You have an established flare there, and if you wanted to, you could grow it as a twin trunk. I don't think any of the others allow you to cut low enough and ensure success. Unless you grafted prior to the cut. You could roll the dice on a cut with 4 (nice natural trunk movement), but 1 and 6 already have sacrifice growth to keep while the cut produces new growth.