An interesting ( if you are petty like me ) issue came up at the last fair we did . One of our customers said that their straight mug kept the contents warmer for longer.
So I did an experiment , I boiled the same amount of water in a straight and the same amount in a bellied mug . The straight mug at 5mins lost 17.2 degrees c, the bellied mug 18.1, at 10 mins straight lost another 7 degrees the bellied 7.5, at 20 minutes , straight 9.1 bellied 8.6, at 30 mins straight mug had lost overall 37.9 the bellied mug 41 .5.
So they both lost heat at more or less the same rate until 20-30 mins when the straight mug was slightly warmer.
Best bet is to drink it in under 10 mins unless you like a luke warm drink.
