The easy button with a $2000 budget: get a Colt 6920 OEM, add furniture of your choice, mount an Aimpoint PRO or Duty, buy a bunch of 30 round magazines and a case of ammo. Done.
Want more money left for ammo out of the $2000? Buy a S&W M&P Sport, mount an Aimpoint, buy magazines and use what's left for ammo.
Don't overthink it. As much as we love to talk about the differences and what the "best" is while online or at the gunshops or the range with our friends, at the end of the day, with most people's shooting skills and how much they actually shoot, the differences don't matter. This applies to AR carbines, polymer 9mm service pistols, bicycles, motorcycles, and many, many other things. Just get the one you like and can afford and make the effort to get good at using it.