Upright pianos made recently are all overstrung and underdamped. These terms describe the layout of the stringing and the position of the dampers within the mechanism of the piano.

The two main types are overstrung, where the bass strings cross diagonally in front of the mid and treble strings, and vertical or straight-strung in which all the strings run parallel.

Overstringing, first used in the 1850s, gives longer bass strings and a more sturdy construction. Also the bridge, which transmits the string vibrations to the soundboard, does its job much more effectively as it is further from the edge of the soundboard. With a few notable exceptions (e.g. certain Bechsteins) vertical strung pianos are best avoided as their tone, especially in the bass, is inferior and they tend to be less stable.

The dampers are a crucial part of the action of a piano. They prevent the strings from vibrating when notes are not being played.

Earlier pianos were often overdamped - meaning that the dampers were situated above the hammers. These were much less effective than underdampers which operate further from the end of the strings and hence cut the sound off more cleanly. Also the linkage that lifts the dampers gives the action a different feel, so for these reasons underdamping is always preferable.

Grand pianos exist in sizes from around 4ft to over 9ft, although anything under 4ft 6in can hardly be considered worth having - a good upright would be a far better choice. The main advantage of a grand piano is that the action (provided it is a proper "repetition" action) can give more control of the volume when playing, as well as faster and more accurate repeating of notes. If looking to buy a grand piano, the main factors to consider are the build quality, type of action, tonal quality, size and condition. It is definitely worth having a good tuner/technician check for these things, or to buy from a reputable dealer/restorer.