Optimized designs of heat exchangers, and, in particular, heat exchangers and assemblies comprising multi-exchangers or combo coolers comprising different heat exchanger parts or elements, and fins or separators of different types and/or characteristics on the different tube parts of the heat exchanger results, are disclosed. The two part heat exchanger is capable of being traversed by different fluids, and fins differ in characteristics, such as height and pitch, to increase overall heat exchanger efficiency.