How to tell different ELM327 scan tools

The ELM327 is a programmed scanner produced by ELM Electronics for translating the OBD interface found in most modern cars. There are as many as 26 various elm327 products are available in aftermarket. They project almost the same function, but differ in some aspects. How to identify different elm327 items and choose a best one?
ELM327 can be divided into different categories according to the different ways
1) Operating system
ELM327 are designed to work on various systems, Android and PC system, Android and IOS system, Android, IOS and PC system, Android and Symbian system, IOS system only etc. Different system based elm327 scanners highlights different features, also differs in software installation and usage. Users had better to pick up one that meets their phone/PC requirements.
2) Connection Mode
ELM327 products are designed to work through multi communication ways, WIFI, USB, RS-232 and Bluetooth.
WIFI:
WIFI ELM327 interface is able to detect and interpret obd2 / eobd protocols automatically. It also provides support for high speed communications and a low power sleep mode. It is easy to communicate with a host device (PC, notebook, iPhone, iPod touch, iPad and so on).

USB:
USB ELM327 scanner can translate all the hard work of protocol into a simple ASCII character based view via the included serial cable. USB ELM327 is used as an interface to connect virtually all OBD-II compliant vehicles to a PC for on-board diagnostics (OBD).

Bluetooth:
OBD-II Software for ELM327 Bluetooth is a free program that allows you to use your PC and a hardware interface to get the information from your car`s computer.

3) Communication Protocol
Some elm327 products are special designed for CAN BUS protocol vehicle models, some fits for OBD?and EOBD? vehicles, most of them support all OBD?protocols vehicles. Make sure pick up a correct elm327 to meet the requirement of your vehicle communication protocol.
How to identify the communication protocol of your vehicle?
As a rule of thumb, GM cars and light trucks use SAE J1850 VPW (Variable Pulse Width Modulation). Chrysler products and all European and most Asian imports use ISO 9141 circuitry. Fords use SAE J1850 PWM (Pulse Width Modulation) communication patterns.
There are some variations among captive imports such as the Cadillac Catera, a German Opel derivative, which uses the European ISO 9141 protocol.
On 1996 and later vehicles, you can tell which protocol is used by examining the OBD II connector:
J1850 VPW–The connector should have metallic contacts in pins 2, 4, 5, and 16, but not 10.
ISO 9141-2–The connector should have metallic contacts in pins 4, 5, 7, 15, and 16.
J1850 PWM–The connector should have metallic contacts in pins 2, 4, 5, 10, and 16.

4) Outlook Design
The outlook design of elm327 scanners turns to get smaller and smarter. MINI elm327 takes over the elm family. Some even special designed with an ignition switch to expand service life. Some elm327 scanners are offered different color alternative.