I have a personal bias against Kohler. While some of their products are quite nice, I disagree with their philosophy - they are a 'not invented here' company. They seem to be constantly changing their designs, often, it seems, just to be different, not necessarily better (does one really need five tries to get a toilet that flushes well? - BTW, there is no industry standard on that, Kohler's class 5 is just a marketing thing, not comparable to anything else in the industry, IOW, there is no standard). As a result of this, their parts book looks like a phone book...most other's change the trim, and have a quality, reliable, easily replaced working part guts so you can actually find replacement parts when it becomes necessary.
Some people don't like the shape of the Toto toilet seats, personally, I find them fine. As to how they work, I think Toto is more reliable. Their dual-cyclone flush is easy to clean, cleans the bowl well, and is reliable. Depending on what you are replacing, keep in mind some of the very old toilets used 3-5x as much water, and yes, they cleaned themselves better than the new ones...a side effect of the water conservation, where the newer ones only use 1.6g or even less, depending on where you live, and your local rules. I've not had issues with my Totos, but some of that is also dependent on diet.
Kohler has some designs that force the waste to turn a sharp 90-degrees at the outlet, Toto's trap design is much more symmetrical. This may or may not be an issue...it is often fairly easy to see if you view the toilet from the side. Some are worse than others.
But, everyone's different, and you may or may not experience any issues with one. FWIW, the MAP tests are a somewhat artificial test procedure...the originator of that test says anything over 500g is great. They flush plastic-wrapped paste, not exactly like the real thing, and some manufacturers optimized their results for this test, and they may not clean as well. The test does not indicate how well it cleans the bowl, only on how much goes down the drain.
KOHLER K-8298-0 C3 155 Elongated Warm Water Bidet Toilet Seat, White with Quiet-Close Lid and Seat, Automatic Deodorization, Self-Cleaning Wand, Adjustable Water Pressure, Nightlight, Heated Seat