Good Evening and Welcome to the Forum,
As nomadkng posted, there is really no "best" lens. There are suggestions for lenses that would work better for the area and type of photography that you are interested in. What is "best" for me, may not - and is probably not "best" for you. You have acquired an extremely capable body, that has few limitations.
What kind of photography are you interested in - landscape, cityscapes, architecture, street, portraits, people, cars,airplanes, birds, animals, family, night, astro, bugs/insects, flowers, panoramas, etc. - the list is endless? Also, a hint at your budget would also help.
I'm going to take a flyer and guess that you might respond with a little bit of everything. If so, folks would probably suggest the kit lenses 18-55 and 50-200 or 55-300, that would cover a wide range of everything - wide angle to telephoto. The Forum has a marketplace - where you might be able to pick them up at a good price, use them until you really determine what lenses really interest you.