unfortunately, its more a matter of...... "how many people can we shut out while applying the same amount of pressure"
The logical answer is bott with 2-5 normally. Normally what happens is since everyone is bott, top and mid on your team want to push their tower because its a free lane at that point. Which is fine and dandy except bott lane then falls fast due to massive shove. Your ally jungler will likely come to try and help, but chances are the pressure will be too great and you will likely end up dieing if you stay. The problem gets even worse because then the ally top and mid panic about bott going down so they try to come and help when all the rest of the ally team is low or dead, which results in complete chaos.
It had nothing to do with tower first blood gold at all. It had to do with winning the game by setting as many enemies back as possible.
Similar to how Singed and Nasus do not care that they die, they just get stacks and make havoc for the enemy team by killing minions and taking whatever towers are open. Essentially making it a 4v5 while the Nasus/singed plays their game of 1 vs minions and towers.