Ok this fight is worth not just voting but also explaining my vote.
My expectations depending on the comparison pics:
1: This one goes to Zara, her pair looks invincible (Hollys somewhat shocked look adds to it).
2: This comparison is Zaras again, two firm lookin pairs but one has the size advantage.
3: Here Holly turns the table, if I look at this picture somehow I imagine them in a bearhug in which Hollys tits bore into Zaras bigger but less firm looking pair.
4: Forth is Zaras again, her compresed pair looks that huge and dense I can't imagine her to lose.
5: In their gym outfit Holly looks more curvy with slightly smaller but much harder tits. Here I have similar thoughts as in 3.
Finally for me Zara prevails in a hands off titfight if Holly donesn't have some sort of joker.
The real winners are the spectators able to see two beautiful and hot women no imagination could create going at it.