This is much like asking which vehicle is the best.
Of course, it depends on what you want that vehicle to do. If you want to carry several tons of material from one city to another, a semi tractor trailer might be the solution. For even more stuff, a freight train would be better. If you are in a hurry, an airplane might be better; For carrying a LOT of stuff, nothing carries more than a seagoing freighter ship.
But if you want a vehicle to carry kids and equipment to soccer practice, a minivan does a good job. If you just want a vehicle to pick up groceries, a compact or subcompact car might be your choice. If you needed to get around a race track very quickly, specially built race cars are a better choice.
It's the same for graphic design software. Asking for ONE of the best is hard to answer. While a lot of photographer will tell you that Lightwave is the best post production photo app, I am VERY happy with my Photoshop. But I wouldn't do any full page layouts in Photoshop when there are so many other apps with better tools to make the job easier. I can do a decent page layout in Illustrator, including it's excellent text tools, InDesign is a much better tool. And I would never consider doing a multipage document like a booklet or book in anything BUT InDesign. (I was trained in Quark but I left that behind a long time ago) For photorealistic images created from scratch, Illustrator is the EXACT tool needed.
I wouldn't compose an extensive text document in anything BUT Microsoft Word. Or graphing data in anything but Excel, or simple 2D animation in anything other than Flash.
Do you get the idea? The BEST tool to use in ANY application is that tool that is created to DO that job the best. As a graphic designer, I keep a well stocked tool box in my computer. Like a master carpenter, I may realize that I can drive a nail with the flat end of a box wrench, a hammer can do a much better job of it.