Basically, there are three different "types" of DAQ amplifiers:
Single-ended amplifiers: Single-ended is easy to use, but it has two major disadvantages: unwanted ground loops and non-isolation.
Differential amplifiers: Differential one is the most common and amplifies the voltage difference between two inputs
Isolated amplifiers: Isolated amplifiers are isolated from the housing and the main board of the measurement device, and allow safe and reliable operation.