Had to vote other because I never really ever buy pre-recorded movies on any format. (I have had both VHS and Beta machines). Technology changes pretty fast so eventually you will have to replace your movies on DVD/Blue Ray with the next format. That said. I rent from Redbox, borrow from the local library (free) Netflix and Amazom primarily.
Side note, the next "format" is already here. Instead of the standard 1080p, TVs are now being produced to display 2160p, four times the resolution of Blue Ray. I do not know of any sources for 2160p yet.