Polyclonal

Polyclonal antibodies recognize multiple epitopes on one antigen. They contain a heterogeneous mixture of antibodies with varying affinities. Polyclonal antibodies are relatively quick and inexpensive to produce, but they can be non-specific and encounter lot-to-lot variability.
Polyclonal antibodies are suited for certain situations, like amplifying signal from a low expression target protein. Recognition multiple epitopes, makes them useful in immuneprecipitation (IP) or chromatin immunoprecipitation (ChIP) experiments, and they are tolerant of minor changes in antigens, such as polymorphisms, heterogeneity of glycosylation, or slight denaturation. Polyclonal antibodies can also be used to identify proteins similar to the immunogen protein across tissues or species, and are preferred for detection of denatured proteins.

The downside to polyclonal antibodies is that there can be high variability between batches, they sometimes give high background signals, and their multiple epitopes make it important to check for cross-reactivity.