Doffy also has some level of Regenerationn and can turn the battlefield into threads that he can control at will. It would be incredibly hard for Erza to get herself, or a weapon close to him due to his ability to create traps, razor sharp threads, and turn the floor into threads while the sky above has a bird-cage to limit movement to a degree.
Some may argue that Erza's weapons would cut through Doflamingo's waves of threads, but that would make matters worse for her since Doflamingo can still manipulate threads that are not directly connected to him, such as when he used techniques like enclosing the bird cage, Fullbright, and parasito. Doflamingo can make clones out of string to cause confusion and have them fight alongside him, he can turn the battlefield into threads and put a bird cage up to limit any aerial abilities Erza may have, he can control her body by using Parasito, he can use his own threads to repair life-threatening damage such as when Law used Gamma Knife and caused an explosion within Doflamingo's torso, and he can fight at any range between melee and several kilometers.
If speed is equal, I find it hard for Erza to tag Doflamingo, especially when Luffy, who has proven to be capable of blitzing Doflamingo from a distance, took over 20 minutes to land Leo Bazooka on Doflamingo, despite the latter still recovering from fresh injuries inflicted by Law.
Color of Observation gives its user 360 degree vision and pre-cognitive powers. Doflamingo displayed this ability during the first half of Dressrosa when battling Sanji and Law. Equalized speed for Erza = she will not be capable of tagging him with a single strike unless Doflamingo is in a position where he can not dodge or counter.
I've always seen Erza going extremely aggressive in all of her fights, and Doflamingo is the type to take advantage of this. Even if we consider Erza being stronger than him, his powers and manipulative manner are enough to throw her off. Examples being when Cobra poisoned her and Kaguya successfully countered her initial assault. She only fights with caution once the fight has proven extremely difficult for her AND she is fully intent on winning.
If Doflamingo is in a tight spot, he can fall back on relying on his power's environmental advantages and continue trying to catch Erza in his web of strings and heal any cuts Erza may have applied--quickly reducing the damage she deals to him considerably.
Of course, there is still a chance that Erza may be capable of chopping off Doflamingo's head, but I see Doflamingo's use of hit-and-run + clone trickery catching Erza off guard for him to land crippling blows being more likely, especially due to his precognition and mind-set.
I vote for Doflamingo, but it doesn't matter since that makes it 7-2 LOL