Here's a breakdown of popular evergreens suitable for use as cut Christmas trees:
Balsam Fir or Canaan Fir - It is usually the most reasonably priced and abundant cut tree. Dark green with a slight silvery cast, Balsams have short, flat, needles that are long lasting. Very fragrant when first cut.
Colorado Blue Spruce - They range in color from dark green to powdery blue, with stiff 1 to 3 inch needles. The needles can be so stiff they scratch, so be careful when handling. Good needle retention, but they will drop in a warm room.
Douglas Fir - A beautiful, full dark green to blue variety. It holds its needles well and is very fragrant.
Norway Spruce - Pretty tree with pore needle retention.
Scotch Pine - This is one of the most popular Christmas trees. The branches are stiff with ridged, dark green needles that hold for four weeks and don't drop when dry. As a bonus, Scotch Pine has a nice, lasting aroma.
White Fir or Concolor Fir - This Fir is relatively new as a Christmas tree and becoming increasingly popular. The blue-green needles are 1/2 to 1-1/2 inches long with both a nice aroma and good needle retention. A very attractive tree.
White Pine - White Pines are having a difficult time right now. When healthy, they will retain their blue green needles throughout the holiday season. They make a very full Christmas tree. Because they have little to no fragrance they are a good choice for people who have allergic reaction to the spicier trees.
White Spruce - Similar to the Colorado Blue Spruce, this pretty, bluish green native of the Northern U.S. holds it's needles well, but they have an unpleasant odor when crushed.