You should consider all the boots every game depending on the enemy team.
If you are fed and want to chase for more kills, you would choose between mobility or swiftness. Now if the other team has people like let's say Shyvana or Amumu that can run away while damaging you, then you would choose swiftness.
If the enemy team is cc heavy with/or ap, you should probably go mercury treads. If enemy team is ad heavy with/or auto-attack dependency, you should probably go with ninja tabi.
Now for berserker greaves, it really depends on how you build shaco. If you're going for more of a burst type build, berserker greaves might not be your best choice. If you are going to be autoattacking (which will be hard to do in team fights as Shaco), then you could consider berserker greaves while keeping merc treads in mind.
Hope this helps.