Last thing to consider is the volume. Just how much coffee are you going to be carrying around in this thermal mug of yours? Getting a cute little 10-oz mug isn't a great idea if you want your coffee to last through an hour long commute every morning. A large travel mug means you can bring more coffee, but that doesn't mean you have to. When in doubt, get a thermal mug a bit bigger than you think you will need. And speaking of that morning commute, if you do intend to use your perfect travel mug in the car, you should double-check that the cup holder in your car will fit the base of your new mug. Most cup holders are pretty standard and therefore most mugs are designed with a narrow base so that they will fit. Most is definitely not all, and it would be a shame if your great mug won't fit properly in your car.
Thermal coffee mugs can actually save you money, and even help the environment too. By taking your own coffee on the road, you will save the cost of having to stop at an expensive coffeehouse and you won't have to take any of those disposable paper cups (and cardboard sleeves) either. Really, its a win-win situation so you should invest in a good thermal mug for your coffee-on-the-go.