Which is better server? Dedicated server or Cloud server?

Depends...You could easily get the same resources and capabilites on a virtual cloud server these days as you would with a physical dedicated server, even if the physical server hosting them doesnt have the required compute resources to sustain it, it can easily be migrated to another one online. But are you thinking of leasing a physical server or co-locating one? When co-locating a physical server that you bought, the difference here is you have ownership of the asset (albeit a depreciating one...), whereas with a leased dedicated server or cloud server you dont own anything but the data you backed up and once you stop paying, the service ends. 

Technically speaking, there is no longer any difference, financially speaking, there is. With a dedicated server, i can easily install ESXi, KVM, or Xen and split it into multiple virtual machines/cloud servers, giving me more bang for buck, provided of course that i have the required compute resources needed to sustain them. 

I wish you elaborated more on your question. :)

One point is missed by all.

Virtual server has one faults, it resources is shared. IF by chance some untoward failure comes whether be it in  H/W,N/W  all the systems would be at the fault. This is certainly not in the case of dedicated servers. 

But all the major companies like Google, Microsoft and Oracle are moving towards Virtualization. IT gives benefit to user in licensing also. As the licensing cost is skyrocketing it is quit but natural for the industry to move towards VIRTUALIZATION.

Cloud server is the better server. 

Because there will be reliability, there is no more virus affection or hackers.

Eg : Microsoft Azure

If your resources like internet bandwidth,Power and etc are more reliable than dedicated is best.You can also use clud as a DR site.

Dedicated Server.

Its under our control.We can easly maintane it. But cloud server we can access to any device from anywhere