1D scanners will read any of your linear bar codes, including UPC, Code 39, Code 128, etc. at no more than a 30% Skew and need to see all of the lines of the bar code. Additional height on these lines, merely gives you some error correction.
2D readers take a picture like a camera and then determine what they are looking at. 2D scanners will read all of your 1D codes in any orientation, as long as they can see the entire code. They also can read all of your 2D codes, such as Datamatrix, MaxiCode, QR Code, etc.
Same as the 2D Scanners above, but without the cord. Data is transferred directly into the PC via either a direct BlueTooth connection or via a dongle/base station plugged into the PC via a USB Port. The data will go in at the point of the cursor, or it can be programmed to hold onto the data to until it is placed in a cradle, or a dump bar code is scanned.