Best? As in Fast?
Haha. I say "best" in overall execution and as a holistic product. Unless you're looking for performance and acceleration, the ESh is pretty much perfect: Priced like an IS, more room than the LS, it has every reasonable luxury feature, the latest technology, it looks good and it returns 40+ MPG.
The LS is too compromised - the powertrains aren't a match for the platform, the suspension changes they've made over the years have dulled the agility and sharpness of GA-L and the interior isn't very spacious. The design, drive and demeanor of the car don't match, IMO.
The IS benefits from the "New N" platform being one of Lexus' best, but it needed to be all-new in 2021, not refreshed. It also badly needs new powertrains... IS 350 (2.4T), IS 350h, IS 450 (3.4L), IS 450h+, etc. Lots to love about the IS, but Lexus has done as much as they can with an old car and platform.
The ES, the more you live with it you realize, is nearly perfect. Both the V6 and the hybrid are well mated to the chassis, suspension and demeanor of the car. The hybrid has enough power and makes up for the horsepower disadvantage from the V6 with smoothness and MPG. The interior is shockingly nice and has very thoughtful details: Levinson speaker grills, quilted leather, soft touch points, different colors and textures of materials on the dash and doors, the new headlight and grill shapes are beautiful together, sun shades, ML audio is great, 12.3" screen is well placed and well integrated, trunk is huge, the list goes on.
The ES isn't making any qualms about just being a fantastic luxury sedan, and it's the only car where Lexus didn't try to make that formula into something different. It's very succinct and clear in what it is, in a way the new LS is not and the IS cannot be because of age and technology.