Hmm.wrote:* Ancient Earth Elemental (T:10)
Hit Points: 381
AC: 24
Saves: (F) 24 (R) 12 (W) 13
AB: 29/24/19
Damage: 4-32+12 (19-20/x2)
Feats: Blind Fight, Cleave
Properties: DR 10/+5, DR 15/+3, DR 2/-, 25% Physical Immunity, Immunity: Knockdown
* Ancient Water Elemental (T:10)
Hit Points: 243
AC: 28
Saves: (F) 18 (R) 20 (W) 13
AB: 27/22/17
Damage: 4-32+10 (19-20/x2)
Feats: Blind Fight, Cleave
Properties: DR 10/+5, DR 15/+3, 10% Physical Immunity, 100% Fire Immunity, Regeneration +10
Special: Aura grants allies +7 regeneration per round
In order of offensive strength, the elementals go Fire > Earth > Water > Air.
Earth certainly does not kill slower.
Water was intended to be the all-rounder (with sustain), so falls lower on the offensive spectrum. Which isn't to say it's not a bit overtuned.