Pick the one with the best graft union, or the one you can hide the easiest if you want one of these you've shown us. There are some with better grafts and some with horrible ones, these are about middle ground... But I like the shape of the last one, just cause it's a bit different than the norm, and I like the flair at the base, nice taper too. Looks like you could do some creative shaping with it, and minimize the graft. First one would be my second choice, as there are branches you can shape near the graft to help.
I have not had a hard time with these trees as others have had, just be conservative when you repot... They are not fast to develop, so don't expect too much too soon.