I'd say 10, since it does have some good scenes, but the plot makes little sense if one thinks about it, and it does have some continuity problems. I've not see any after 10, and I only have the first 11 on dvd with 11 up for being watched this friday or weekend. Part of 4 would be listed on my list. Overall I liked the movie, but it has a section that is a large problem, Ali able to travel such a long distance in minutes, unless all longneck farwalkers can do that even while taking others with them, which would mean Littlefoot & his mother and grandparents don't in the first movie since being residents they can't travel like that. The who needs you song, taken out of context I enjoy the song, but kept within the movie feels to me like it does not fit. In the middle of a mainly serious scene the 2 villians decide to do a stand up comedy routine. What if some of the aliens had decided to do that in the aliens movie.
Overall I'd say 10. Some others may have either small errors or ones I've not noticed. Part of 4 would be up on the list, but not 4 overall.