All of the toilets mentioned have good fill valves in them.
Often while working on tanks, I wind up using either the Fluidmaster or the Korky.
I prefer the Korky, but that's mainly because I like a quieter fill without water hammer.
If don't mind noise, go with the Fluidmaster. Nobody ever got fired for buying IBM, but it was Microsoft that won the day.
In your experience are these larger flush valves as reliable as the standard size ones? I ask because the sales guy is recommending the larger flush valves because of the added flush power but on the net there posts of the seals leaking/getting soft plus the repair parts are less common.
I sell more TOTO than anything else. They have been very good with the 3" flapper and flush valve. They were the first with it.
American Standard's first 3", was a tower setup that has been discontinued. They have gone back to a solid backed flapper. That's not to mean that the seal doesn't need replacing like any product submerged in water.
Koher's first venture into large flappers was their 3.25". They have gone away from that and now use a canister over the seal. They cut down the size at the same time. It's fairly new, so it's too early to say anything.
The Flushmate pressure assist, when it needs work, has more to do with keeping the inlet screen clean so that the tank will build pressure to flush, and the duckbill assembly. The main cartridge will last a while.
All flappers need replacement at some time. The old 2" flappers made of black rubber went bad very quickly in some areas. A longer lasting 2" flapper was made with Red Rubber, or whatever they actually put in it to resist chlorine. Those were called five year warranty flappers.
Generally, keeping any toilet tuned is simple and involves little cost. I can't tell you how many homes I've been in where you can hear water running from the front entry way. Most people seem to tune that noise out.
Standard black 2" flapper with one year warranty
To flush a toilet with a small amount of water, you need a spurt of water fast. There are basically three ways to do that: larger flapper, pressure assist, and larger pipe (generally only used in commercial units because the average home doesn't have the water pipe size required). The goal is to get the water moving fast enough to create a siphon so it can carry the waste efficiently out of the bowl and then shut the water use off so that it stays within the mandated max. Older toilets may have used as much as 8 gallons or more and took their time about it. Getting it from that outlet point to the rest of the drain is important, too, since the shape of that trapway will affect the velocity and whether things need to slow down as they exit. This is where smoother curves are better - for less restrictions to keep the speed up, and for minimizing clogs in case you're trying to flush brick hard logs. The size of the trapway is important, too, but since most people's waste is at least moderately pliable, you can get by with a less optimized design most of the time. To get a super large trapway, you need just that much more initial water velocity (assuming the same amount of water is used) to get it to siphon and clear the bowl. One reason the Caroma may splash a little (flush after you get up!). Getting all of the pieces right and making a reliably good product points to the winners in this race. Some get it right on a regular basis, some don't. Since everyone's different, what works for one may not work for another. There is no one toilet that will work for everyone because their priorities are different: style, color, size, performance, cost. The experience here, and mine personally, is that for me anyway, Toto both performs well, and fit my needs. That may not be true for you. But from a reliable viewpoint, and parts availability and ease of eventual repair, unless you get one of their exotics that can cost into the thousands of dollars, they are easily serviced with readily available and inexpensive parts. This isn't necessarily true for others (it varies from easy like the Toto, to a major pain on some others). Any time someone comes up with a new design on a flapper or fill valve and it's proprietary, or not common, you're asking for at least an annoyance, if not plain trouble and maybe excessive costs.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013
Some other proprietary seal designs, like the AS Champion, may be a little more hit-or-miss in terms of replacement part availability and ease of repair.
When I bought our two Drakes, I also bought a replacement flapper which I put in the tool drawer for whenever it is needed. Haven't needed it yet.