Here's my worthless take on the subject:
Rob Cosman uses a 5 1/2 as his main bench plane, but his teacher was also Alan Peters....
I'm always leery of any advice that unequivocally states this is the best for "you" ;-)
When I'm preparing a common width board as a reference face, something 4" or wider, and more than 12 inches long, my go to smoother is a 5 1/2. It's also my workhorse for joining panels from those types of boards...may switch to one of my infill panel planes if it's difficult grain, but that's because I have them and they work on difficult grain.
Beyond that Kees is spot on, and for me it could be a tiny wood smoother, and infill miter, or a LN 4 1/2, or any of many other smoothers. My go to "Kees" smoother that lives on the bench is a Voigt coffin.
With all that rambling, the real answer is:
It depends ....and that's a huge spectrum of variables and causalities LOL