I'm not certain of the differences between Algerian and Italian, but I can tell you some of the main attributes of Algerian.
- light in color
- grain doesn't have much contrast unstained
- can be contrast stained with excellent results
- birdseye tends to be somewhat loose
- blasts evenly without much ring detail unless you develop some techniques for bringing it out
- very neutral flavor
- tends to have a lot of very small pinprick flaws, of the type that can be hidden with a contrast stain
- relatively free of larger flaws
- very light and not as dense as some others (see note about blasting above)
- ring grain can be very apparent when stained and finished smooth
In contrast, my experience with Spanish briar:
- slightly darker in color, though still a creamy tan when well processed
- light contrast in grain when unstained
- contrast staining may need extra attention due to it's density and slightly darker coloration
- blasts easily with good detail and depth
- can have an interesting, yet very subtle, flavor that seams to compliment darker tobaccos like flakes and cakes
- pinprick flaws common
- larger flaws are a little more common, but are easy to work around
- much denser wood, and makes a heavier pipe than Algerian briar of the same size
- ring grain not as evident when finished smooth
I am not experienced with Grecian or Italian briar.
All briar is root briar. The root ball is a big burl of wood, and this is where the briar blocks are cut from. I've got my popcorn ready for the inevitable discussion of "dead root" briar....
Shell is a Dunhill finish - sandblasted, essentially.
The main difference you will see in briar blocks is the shape and the existence of bark. See this page:
http://www.pimopipecraft.com/briar.html
Some places (most actually) refer to blocks for straight pipes as "MF" followed by a number indicating size. Blocks for bent pipes are typically "R" followed by a number indicating size. I tend to use MF3-4 and R-2/12 for most pipes. The plateaux is where you'll get most straight grained pipes from, though I have gotten one or two from inexpensive MF blocks. These seem to be sold by weight here in the US, but most cutters in Europe sell them by size. Some cutters actually use "R" sizes for plateaux.