What’s the most efficient network setup?

I have an NT network with a PDC, BDC, and 3 member servers. A firewall, 30 Workstations, 1 Switch, and 4 Hubs. I have all the hubs going to the switch, I want to know if all the Servers should go to the switch also or stay in the 2 hub they are now in? What is the logic for either, in making an efficient system?