QR Code	DataMatrix	Maxi Code	PDF417
Developer	Denso	RVSI Acuity CiMatrix	UPS	Symbol Technologies
Type	Matrix	Matrix	Matrix	Stacked Bar Code
Capacity: Numeric	7'089	3'116	138	2710
Capacity: Alphanumeric	4'296	2'355	93	1'850
Capacity: Binary	2'953	1'556		1'018
Capacity: Kanji	1'817	773		554
Main features	Large Capacity, small size, high speed scan	Small size	High speed scan	Large capacity
Main usage	Logistics, Factory automation, Mobile phones	Factory automation	Logistics	Office automation
Standard	AIM, JIS, ISO	AIM, ISO	AIM, ISO	AIM, ISO

Sources: Wikipedia, Gerhard Fasol


Big advantage of QR Code:
QR Code is capable of 360 degree (omni-directional), high speed reading. QR Code accomplishes this task through position detection patterns located at the three corners of the symbol. These position detection patterns guarantee stable high-speed reading, circumventing the negative effects of background interference.
Source: TechnoRiver