Today, there are many different types of veneer available on the market. Veneers can be generally organized into two categories, Flexible and Standard. There are significant differences in cost and ease of application, that I will briefly describe in the following.
Just as every tree has its own character, so does every individual sheet of veneer. When veneer is cut from a log, the manufactures are very careful to stack each sheet in the same order as it was cut. If this care was not taken you would be unable to purchase two or more sheets almost identical. This is crucial if you need to joint two or more sheets together to create a wide matched panel (even if matching sheets have some variation in grain and color). So, pay the appropriate attention that your supplier offers consecutively sliced sheets of veneer.
Standard veneer has been around for more than one century, getting thinner with the passing of time, the progress of cutting equipment, and the exploitation of the world's forests. The sheets are cut from a log, stacked in consecutive order, then sent to a drier. Years ago, most Standard veneers were cut to approximately 1/16" to 1/20" thick. Today most Standard veneers are cut to a thickness of about 1/28" to 1/40". Depending on your source of supply and were you are located in the world, certain species of veneers can still be found in thicker sheets. In Italy, the almost only veneer available in thicker sheets is mahogany (mainly used for the outside face of front doors). In more lucky countries oak, black walnut, maple, cherry, mahogany and some others can be found.
Standard veneer is usually available in random widths ranging from about 3" to 12". Some species like white and red oak (North America) and mahogany which grow in larger diameters are available in wider sheets. Available lengths vary between 3 and 10 feet, with many species only available in short 3 foot lengths. Don't forget to negotiate with your supplier (and maybe also to visit the warehouse with him/her in order to select the sheets), so that you buy what you really need. Since Standard veneer is usually sold by the square foot, suppliers tend to get rid first of the small cuts, less attractive, but this might not go along well with your needs. While it would be a waste to insist to buy large cuts when you know already you'll be using them to cover small surfaces, do not accept to buy small cuts that will cost you time and patience to match if you have to cover large areas.
Standard veneer should be purchased in consecutively sliced sheets and of good quality: relatively flat, with little or no knots or sapwood, uniform in color, with very few or no checks or splits. There are some exceptions to this like certain highly figured veneers. Burls and crotches cannot generally be found in perfectly flat sheets, free of splits or some knotholes. This is because highly figured woods are hardly stable and tend to warp and buckle much more. Of course, these particular types of veneer take much more preparation for flattening, filling knotholes, and taping the sheets before gluing them down.
The price of Standard veneer varies significantly depending upon species and varieties. Also, it depends upon were you live. But, in general, I find veneer cheap and flexible, and definitively enjoyable to work with. Finally, when working with Standard veneer, make sure to purchase at least 20% to 30% more than what you actually need, in order to factor in waste and excess for trimming and jointing.
This new type of manufactured natural wood veneer product was first introduced about 20 years ago, and it has been gaining popularity ever since. Flexible veneer is manufactured by slicing very thin sheets of veneer (approximately 1/64" thick), treating the veneer to make it more pliable, then the sheets are jointed together and permanently mounted on a paper backing to bond them and give more flexibility. The result is a wide sheet, with already matched patterns, and ready to be trimmed and glued.
The main advantages are:
Because the actual veneer face is so thin, Flexible veneer cannot take much sanding. Once the Flexible veneer is glued to its surface and the glue has cured, it can take any finishing, just like any other veneer. Obviously all this convenience has a price. Flexible veneers are, intuitively, more expensive: typically two or three times the cost of the Standard veneer of the same spice.
I would suggest to limit the use of Flexible veneers when large areas need to be covered. This because of the time saved and the sure, clean result. But if your piece is made by small surfaces, Standard veneer is just as good and so much cheaper.
Cracks, checks and splits: cracks are not necessary evil. If there is no missing material, cracks disappear completely after a careful gluing of the veneer.
Holes: Small holes can be filled with some wood paste after the gluing and curing, and before general sanding. Large holes need to be filled with a piece of the same veneer, possibly matching at best the grain.