Tis an excellent question, I have a 2 quart Stanley about 10 years old, a 1 litre nissan medium mouth about 7 years old, a Thermos brand 1 litre about 17 years old.
I had a uno-vac that was old when i bought it at a yard sale 20 years ago, sold it in another yard sale about 5 years back [replaced it with the nissan] to keep anything warm for any length of time i used a pair of old poly propolene socks on it and used the coffee out it first during the day... the whole unit outside was stainless, and would be toasty warm not to long after the boiling coffee was placed inside.... the vaccum seal probably was not proper on it although when submursed it never gained any water inside.
The 2 quart stanley was purchased because my mother worked at a hardware store and could get it for cost [then $35] instead of retail of $55, thought it would replace 2 - 1 liter/quart bottles.... wrong.... coffe stays hot, but as it is drank, the remaining coffee gets cooler and over 8 hours for the going home drink of coffe at the end of the day is luke warm. Mom bought 3 of those, and 2 of the 3 were that way, the other one held a few degrees better... of course she sold that one cause dad and i did not need 3 units!!!! A friend had one fall off his back hoe, and 3 days later it was just as hot as it was the day he buried it [found it when he was back filling the ditch] again showing that if insulation is added, it holds heat longer.
The nissan was purchased actually for taking soup out overnight on hound hunts, when I figgered out that noodles swell larger if left over night, i did not use noodle soup in it again.... however it holds heat the best of all the jugs I have, the lid on this model has a problem, it is not a one piece and it pops apart for cleaning, and has an additional pour spout screw in lid, if the lids do not fit just right it pops apart when tightening them down.... and of course mine is warped but that has not affected its preformance in retaining heat..... I chose it over the wider mouth stanley at the time because of the additional pour spout even though it was to be a soup jug.
The thermos jug was a gift, and still holds heat better than the big stanley 2 quart, the Thermos has a lift out pour tab, that can be pulled apart and washed when it starts to leak, I generally do not use it and just unscrew the lid to pour, from fear of breaking the tab off or wearing it out... which is probably unfounded but a person ever knows.
The cup that came with the Thermos actually is the biggest of all the units, with the uno-vac being a close second followed by the nissan. The stanley cup is the small traditional looking cup ..... i should say i hardly ever use any of the cups except for holding in heat, i have a stanley/alladin [could be prejudice here] insulated "go" cup ive had for about 10 years... gets washed once a year unless wife finds it sooner, and then it tastes bad [like soap] for a month.
So in answer as to which is best, from my limited experience with only one of each, I have to say over all the Thermos has held best, And i know of people who hav had the 1 quart Stanleys that wore the cup out and the units still hold heat better than the 2 quart models.
And i still want to try the 1 litre Stanley wide mouth for rice cooking and such
www.kurtsaxon.com <---- site you suggested a couple years back... and the reasoning behind the wide mouth is that a spoon can get into one of those easier.... i still think heat loss might be a problem with the wider mouth as they are only plastic/nylon construction for the lids. and at $20 +/- it really would not be a bad investment and problably could be sold for at least half at a yard sale ifin it didnt work out.
The "stop and robs" around here have stainless pump pots that see to keep the coffee hot, and are larger, can be purchased at resaurant supply houses, do not know anything of the cost except that usually the cost of commercial equipment is somewhat higher than consumer units.
