There choice between HotSpot compilers should be made automatically and optimally for 90% or more of typical server Java applications. The runtime should use information about the machine configuration and other information to make this choice.

For example, when the user specifies a large heap this is an indication that they probably want C2. When they're running on a machine with many CPUs, again they probably want C2. When the machine has little physical memory they probably want C1. Other info may also be useful.