Sitka Spruce is the most well-rounded tone wood and is used on more guitar tops than any other wood. This is due to the tonal qualities and sonic projection of spruce. It has a nice even tone and does not accentuate any frequency above another in an overpowering way. Spruce also has a strong attack and does not get muddy at high volumes. This makes it a very versatile wood and makes those players with soft touches sound great and people playing with other instruments cut through the mix.
The auditorium body shape is probably the newest body shape for acoustic guitars. The auditorium takes elements that players love from various other shapes and combines them into a single body. The sound will be slightly different than a dreadnought and will scoop some of the mid range but it maintains the full dreadnought sound. It has a skinnier waist, much like a grand concert. This allows the guitar to rest lower on a player's thigh when sitting down and does not put as much strain on the shoulder. It's not hard to see why auditoriums have gained popularity so quickly.