I think the most specialized faction will be Daggerfall (you have a very solid tank race, a good caster/healer race and a a very solid stamina weapon DPS race). I like the balanced spread of three highly specialized races so this faction gets my vote. I think this faction will have a surplus of heavy melee tanks (for PvE it is a good faction if you plan on playing Healer).
Ebonheart Pact get two good tank options (Nord and Argonian) and a good race for mixing stamina weapons with magicka abilities in Dunmer. No clear cut healer race (but the restoration staff XP bonus on Argonian will probably attract quite a few healers to this faction) and no clear cut stamina weapon DPS race either. I think Dragon knights and Templars will be common on this faction (so for PvE it is a good faction if you plan on playing Sorcerer or Nightblade).
I think the Aldmeri Dominon faction will have a serious lack of heavy PvE tanks (but they have a very solid caster/healer race and two good stamina weapon races that also get sneak advantage). If I were to plan on rolling a Tank I would pick this faction and roll a flame based altmer draconic power + ardent flame one hand and shield heavy tank. I would be in great demand in this faction unlike both the other factions that will probably have a surplus of heavy melee players. I think Sorcerers and Nightblades will be common on this faction (so for PvE it is a good faction if you plan on playing Templar or Dragon knight).