Many of the "large capacity" cups/mugs have a taper on the inside. Some of the worst actually have a "globe shaped" innard. The problem with this is that you have to pay attention and tilt your head back to a different angle when the amount of coffee in the cup changes.
A good mug should be capable of totally autonomic and unconscious use.
You reach vaguely in the general direction and it "leaps into" your grasp.
You draw it close while peering over it at what you're working on, and tilt the cup until the nectar touches your lips.
You satisfy your need, and return the cup whence it came.
If you have to adjust your grip, tilt your head, or in the worst cases actually lean back in your seat to get to the last dregs, it ain't a righteous cup. The only good shape for the inside is a straight untapered cylinder.
The "superwide base" things are intended mainly for use in vehicles not equipped with "cup holders" and are really useful only if you need to set them on the dashboard (or on the seat beside you). The wide base resists tipping. You can also get them with a "sandbag base" that will conform to almost any surface. For safety, a cupholder and a more conventionally shaped cup is really better.
Since a good "sipping rim" is about 3 inches in diameter, I'd have to clear a large bit of my workspace to use one with a 3x (9 inch diameter) base. No thanks.
Unfortunately, cups with lids (to prevent splashing in a moving vehicle) all are (so far as I've seen) plastic, at least on the inside. I may have an unusual sensitivity, but I've never been able to enjoy my nectar from any plastic container. I detect an objectionable taint even from most paper cups - especially including those used by Starbucks.