Clay golem gets a crazy life bonus.
With a skill level of 21/21 for all golems and mastery (with skill adders not placed points):
Golem life
Clay-11,550
Blood-3,312
Iron-5,146
Fire-5,318
I find this strange but it's true. It's gets further ridiculous at higher levels. Check out these numbers.
(Skill points 40/40/40/40, Clay, golem mastery, Blood, Fire):
Golem's life
Clay-40,287 [Ed's note: !!]
Blood-5,740
Iron-9,800
Fire-10,130
The strange part about clay is that his incredible life is not dependent upon synergies. It's just his natural bonus.
This 'little' benefit is also considered to be bugged at this time but no official word from Blizzard has been heard from my knowledge.