I recently read this interesting article on Aikido Journal by Toby Threadgill, entitled "Assumptions."
It begins: "Recently I was introduced to a gentleman interested in martial arts training. He was not really aware of what I teach or of what constitutes Nihon Koryu Jujutsu. He just assumed that because I taught it, that I must believe it to be “the best”. When I told him I did not believe the art I taught to be “the best”, an uncomfortable silence ensued. I finally broke this taciturn moment by explaining that there is actually no such thing as a “best” martial art."
It's a nice article, and I don't think I could improve upon it by anything that I say. Ultimately, no one is bulletproof. No art art will save you 100% of the time under 100% of circumstances. And the purpose of studying any given art will be vastly different from a police officer to a retired school teacher.
In terms of practicallity, it's almost like saying a hammer is the best tool out there, and certainly better than anyone else's tool. Sure, as long as you encounter nails and things that need to be whacked in general and maybe pried apart with the back claw. But a hammer can't do what a saw or screwdriver can.
In terms of an art, well, such petty suppositions get even sillier. It's like saying Monet is better than Picasso. Better at what? They paint in different ways and set out to accomplish different things—but both wonderful and beautiful, and both changed the way the world looked at art.