With the instrument possibilities suggested by this form, next use the appropriate exposure time calculators available using the IRAF spectime package to decide which is the best instrument for your project.
Multi-object capability -- not an option in this form -- is available with hydra on WIYN and with multislits on the RC Spectrograph and Cryogenic Cameras on the Mayall.
The recommendations from this form should not be regarded as the final answer. Specifics on instruments are available in the Telescope and Instrument Documentation section of the KPNO Web pages. The Low-to-Moderate Resolution Spectroscopy Manual is of particular note as information is included on all appropriate spectrometers and trade-offs are discussed.
To get answers to your questions see the appropriate contact person for your instruments and areas of interest.