Tobacco cuts whats the difference?

Plug tobacco is tobacco that's still in a block and you can use a good sturdy knife to cut off whatever amount you want to smoke and then use it like a flake. A flake is made by pressing the leaves together into a block and then finely slicing them. Flakes can be smoked one of two ways, either by folding it in half longways and then in half the opposite way and loading the pipe (I prefer this method and then rub the bottom out a bit between my fingers to help with draw), or just rubbing it out completely to get more of a ribbon like texture. Ribbon cut is already cut down into fine small strips/ribbons and is the most popular way blends are made.
My guess as to why "all" brands don't offer a variety of different cuts would be cost. The more established pipe tobacco companies like Mac Baren, Peterson, Samuel Gawith, G.L. Pease, and so on tend to offer at least two or three different cuts.
As for best for self blending, which I haven't done yet, I'd venture to say ribbon cut might be the best to start with. Then maybe phase yourself into adding a cut plug or broken flake when you start getting the hang of things.
I've only had ribbon and flake cuts. The flakes tend to have a more intensified flavour to me. My guess would be because of the pressing of the leaves that's involved. Also some say flakes are better to smoke outdoors, because they tend to stay light in the wind better than ribbon cut blends.
Which presentation is better will always be subjective and completely a preference to the smoker.
Definately suggest giving a few different styles of cuts a try though.

Here are some brief descriptions from the Lane Limited trade brochure.
Pipe Tobacco: Standard Cuts

Most pipe tobaccos, and the majority of the pipe tobaccos in Lane’s portfolio, are cut following the casing and top flavor process. Here are the most common cuts:
Loose Cut: A long, thin ribbon cut.Commonly found in many Captain Black and Lane Bulk blends.

Broad Cut: The thickest cut, about twice as wide as a loose cut. Commonly used with air-cured Virginia which is then used to blend with other cuts.

Cross Cut: A broad cut that is cut twice, creating small squares.
Pipe Tobacco: Pressed Cuts

With pressed cuts the tobacco is placed under extreme pressure and varying degrees of heat for an extended period oftime. The tobacco emerges in compressed cakes or rolls. A bit of fermentation also occurs during the process, which gives the tobacco a fuller, rounder taste. Pressed cuts usually contain little or no top flavor.
Flake: The tobacco is placed under very high pressure varying degrees of heat. When the tobacco cake emerges, it is sliced into thin flakes, typically about 1-2 inches wide and 0.1 inches thick. You fold or lightly rub the flake to put it in your pipe.

Ready Rubbed: Flake that has been created under slightly less pressure. The flake is partially separated so it can be readily smoked or combined with other cuts.

Cube Cut: Flake tobacco that has been cut into small cubes.

Roll Cake: Flake tobacco that is sliced more thinly than normal. The flakes are then rolled into a tight tube. Finally they are sliced again. The result is a thin medallion.

Spun Cut: A time-intensive process where tobacco leaves are hand rolled into thin ropes as much as 60 feet long. The rope is then placed under compression and ultimately sliced into medallions, similar to roll cake.
Pipe Tobacco Mixtures

“Mixture” is a term often seen on pipe tobacco packages. As the name implies, it is simply a mix of different tobacco types, cuts and flavors.

Usually the finer the cut and the looser the tobacco the faster it will smoke.