Of the twelve Alwars, 3 of them are different from the others. They are Thiruppaan Alwar, Andal (Kodhai Naachiyaar) and Madhurakavi Alwar.
The main difference is that they dont have any criticisms in terms of their work. Thiruppaan Alwar's "Amalanaadhipiran" is a very small and concise set of verses which has all Bhakthi, the crux of the Vedas and the way to Mukthi. On the other hand the other Alwars had written a lot (Hundreds and Thousands) and one have to read all of them to understand the same aspect. Also they sometimes discuss about things other than God or Other Gods instead of the Central theme and make it much longer. In that sense, the 2 other Alwars are also not subject to any such criticism namely Andal and Madhurakavi Alwar.
Andal sang "Thiruppavai" (30 verses) which is the crux of all the vedas and ultimate Bhakthi. Madhurakavi Alwar sang "Kanninum Siruthaampu" (11 verses) in which he sings in praise of his Guru (Acharyan) Nammalvar and he did not even sing about God. He stressed the importance of Guru who can lead us to God.
Thiruppaan Alwar - Was born in Paanar Caste, but was invited by Lord Ranganathan himself to come to the temple on a Sage's shoulder. He entered the temple and the Sanctum Sanctorum and sang in praise of the Lord and his glorious posture in Srirangam, whom he has not been allowed to see and attained Mukthi immediately.
Andal - Was found by Periyalwar in a Garden and was brought up. She was a Child when she sang Thiruppavai and was invited by the Lord himself to come to Srirangam and got married to him and became one with the Lord in Srirangam.
Madhurakavi Alwar - His work of Kanninum Siruthaampu was responsible for getting back the entire 4000 verses of the Prabhandam to Naathamuni. He found Ramanuja much ahead of his days (birth) in the form of a statue, when he tried to make the statue of his Guru with the waters of River Tamiraparani.
So learn the works of these 3 Alwars - Amalanaadhipiran, Thiruppavai, Naachiyar Thirumozhi and Kanninum Siruthaampu.
Praveen alias Sudharsan