Oak is the best. UB's acclimation is amazing but Ooze's attack speed reduction is additive, not multiplicative, so when peope are going from 170% attack speed down to 130% it's not a true 40% damage loss.
Oak just has everything. Minions, +damage from skills, the most effective interrupts, a scaling % damage debuff, an AoE movement/attack speed debuff to make sure his reinforcements win and to make sure his minions get more out of +damage items than you see on the tooltip, there's just no comparison.
Personally I think Sedna is awful late game. He damage is poor and she has no AoE to speak of. Minion swarms crush her and she just doesn't have that many tricks. Sedna is very much a what you see is what you get type of DG.
I'm not especially impressed with EB late game unless he's outfarmed everyone. AoE and reinforcement damage eventually outpace his minions' HP and they don't naturally avoid damage the way spirits do. That isn't to say he's weak, I just think that Oak and UB eclipse him when artifacts come into play.