What type of music do they like to play, and what kind of guitar do they have? These two preferences (especially the first one) will have a huge bearing on what type of amplifier to buy.
Most players prefer tube amps (which are generally more expensive) over solid state amps, even for room-volume practice. Tube amps most always sound and "feel" better, although there are good solid state amps and bad tube amps. However, there are MANY different categories of tube amps, depending on which genre of music you play.