A Grand piano is considered better than an upright piano. Aesthetically I could understand why, but why does the orientation of the strings matter so much sound-wise?
It's all about the size, and therefore the length of the strings and the size of the vibrating surface of the wooden soundboard.
Even a baby grand at ~5 feet is longer than a typical upright is tall. A concert grand at 7-10 feet is much, much longer.
I can't do any better than what Wikipedia says, so I'm going to quote wholesale:
Really tall uprights do exist, but they're not very common. They are sometimes referred to as upright grands.
Of course, whether inharmonicity is good or bad is purely subjective. That classic "pub piano" sound, fits perfectly with some kinds of music. It's the sound of an upright, and probably couldn't be replicated on a concert grand.
Adding to the above, this is the reason why upright pianos went from having strings vertical to being overstrung. This means the strings ,particularly the lower ones, are diagonal across the soundboard.It makes them longer, with the above advantages, but still not as long as those in a grand. 36" on the bottom string of one of my uprights, compared with 42" on my baby grand.
The action makes a grand better.
In a grand, gravity helps the key return so you can play faster stuff. In an upright, the action goes sideways and has to be helped out by, umm, don't quote me on this, springs I think?
And the sound, too.
The sound is more of a subjective thing. But in almost all cases, a long enough grand will sound better due to the wonderful bass sound. Also they open more directly to the room so the string/soundboard sound gets to you more directly (plus the room reflections).
Uprights have to bounce the string/soundboard sound out the back against the dang painted drywall (your wall).
Also the pedals.
Grand pianos have a middle pedal called a Sostenuto pedal, which captures keys which are depressed and lets them ring while keys played after the pedal can play without being held on. Uprights on the other hand have a middle pedal that serves as a "practice pedal" which essentially mutes the whole instrument. Usually this middle pedal is missing or non-functional on an upright.