Taint elementals are elementals, but EVIL!!!! They all have the Evil subtype (but lack the outsider type to make full use of it), have a touch that inflicts Corruption points, are immune to taint, and can use Dimension Door 3/day as a move action. Of note is that their Dimension Door doesn't prohibit taking actions after the teleportation. Also of note is the fact that it doesn't seem to alter the wording that allows for taking along creatures.
Please be aware that taint elementals, while not earth or water creatures, do have the save progression of these elementals.
With basic abilities established, on to the individual monsters!
Small Taint Elemental
2 elemental RHD, surprisingly good ability scores (+4 to strength, constitution, wisdom and charisma), a moderately strong slam attack, good natural armor, and a 1/day bonus to a variety of rolls (thanks to Surge of Malevolence), as well as very good mobility thanks to Dimension Door. This is definitely worth +0, and perhaps even +1, though I'll use the former score for now.
Medium Taint Elemental
4 elemental RHD aren't the greatest, but those stats aren't awful and the party casters still don't have Dimension Door... I'll be nice and assign +0 here as well.
Large Taint Elemental
Yeah, no. 20 strength and Large size is something I can get by being an ogre for half the HD, and at least the ogre would be able to use weapons. -0 LA.
Huge+ Taint Elemental
Nothing to see here, move along. -0 LA.