Tier 1: Hamilton, Alonso, Ricciardo, Vettel, Button
Explained:
Hamilton and Alonso matched each other and have beat everyone else handily since
Vettel is a four time champ
Ricciardo beat 'The Champ'
Button was extremely competitive when paired with Hamilton and won the battle in 2011
Tier 2: Rosberg, Raikkonen, Bottas, Massa
Explained:
Raikkonen is yet to beat or match anyone in Tier 1 when paired together over a full season so Tier 2 for now.
Same for Rosberg quick on his day but beaten too often by Hamilton to be Tier 1
Bottas good potential but needs to start handling Massa more comfortably
Massa, matched Raikkonen beaten handily by Alonso and hanging onto Bottas
No idea where to rank Grosjean, Perez and Hulk right now bottom of Tier 2?
I think you get elevated to Tier 1 by winning a championship or by beating a 'Tier 1' rated driver over a full season. IMO of course.