It all depends on your network topology and port density. If you only need 24-48 ports, all 100base or 10base then a fixed port switch is probably your best and cheapest option. If you are looking to expand in the near future and need a good quantity of mixed ports, ie, gigabit copper, 100base, 10base, gigabit fiber, 100 fiber, then a modular switch is worth the cost. Also where you are putting this switch in your topology matters. Whether it is a user switch or core switch. Other questions you need to ask yourself is will it be just a Layer 2 switch or do you need Layer 3 routing? Will it need VLANS ? PVLANS? Do you need redundancy. (redundant supervisors in modular switches)