I am planning to buy new cisco switch. which is better, one 48-port switch or two 24-port switches?

It depends on your network requirement...

I am thinking you are going for IP switches .Decided which one you are going to buy ? manageable or unmanageable switches?

 

May be you can have a look at the below link which gives all the information of different types of switch supported by Cisco.

http://www.cisco.com/en/US/products/hw/switches/index.html

 

 

Well, it totally depends on the purpose of the switch and your network topology.
Most of the Cisco switches now have non-blocking backplane - meaning that all the ports can perform at wire-rate simultaneously and that there is no over subscription.
So, there is no advantage in buying224 port instead of a single48 port switch w.r.t.
traffic flow.
also224-port switches will be costlier than a single48 port switch.
also, it increases the comparitive management overhead.
This being said, with2 switches you can design the network to provide more redundancy.
So if redundancy for failure is what you want, and if your network design permits it, then you can go with224 port switches with redundancy.
Regards, Niranjan.