There are three types of Arabic keyboards: standard (QWERTY), Phonetic and Holy Quran keyboard.
The standard Arabic keyboard has many variations which are used in different operating systems.

Sakhr/MSX Arabic Keyboard Layout

IBM Arabic Keyboard Layout
Mac Arabic Keyboard Layout
Summitsoft Arabic Keyboard Layout
Summitsoft Extended Arabic Keyboard
The essential pro of the standard Arabic keyboard is that it's popular among native Arabic speakers because it was used in Arabic typewriters and most Arabic people are familiar with it.
The main con of the standard Arabic keyboard is that it's not easy to use unless you are familiar with it, because the mapping of Arabic to English letters isn’t done based on phonetics which would make writing Arabic on any application much simpler.
For instance to type the Arabic letter Alef which sounds like the English letter "a" you would need to press on the key "h" and if you want to type the Arabic letter Ba which sounds like the English letter "b" you would need to press on the key "f" which makes it difficult for the user to remember the position of the Arabic characters in the keyboard.

Sample of Arabic keyboard layout with English symbols
The main pro of the Phonetic Arabic keyboard is that it's much simpler to use than any other keyboard as the Arabic and English letters are mapped based on their sounds.
For example, to type the Arabic letter Meem which sounds like the letter "m" in English, all you need is to press on the key m, and if you want to type the Arabic letter Noon which sounds like the letter "n" in English you would need to press on the key n … etc.
The other advantage of the Arabic Phonetic keyboard is that it allows the users to remap the position of the Arabic letter according to their choice.
For instance, the user could map the Arabic letter Yea to the English letter "e" instead of the default English letter "y" and so on.
The minor con of the Phonetic Arabic keyboard is that it's not well know to a lot of Arabic native speakers as not many software applications are using it yet.
The most famous Phonetic Arabic Keyboard is supported by Summitsoft Arabic Editor Pro and Prem where it not only maps the Arabic to English letters based on their sound but also allows the user to remap the position of the Arabic letters according to their choice. Below is a sample of the Phonetic Arabic Keyboard supported by Arabic Editor Pro and Prem.
Phonetic Arabic Keyboard with English symbols
Phonetic Arabic Keyboard
Quran keyboard is an extended keyboard supported only by the Summitsoft Arabic Editor Prem.
It is designed mainly to allow the user to type all the Quranic symbols either by clicking on the desired Quranic Symbol on the online keyboard or by pressing on the English letter key that presents the symbol + Ctrl + Shift.
The keyboard can be displayed vertically or horizontally which makes it quite convenient to use.
