Comparison of sonars for potential UUV applications presents unique problems for users without extensive acoustic backgrounds. This paper presents a methodology for sonar selection tradeoff studies as well as evaluation of performance capabilities of several available units. Included are side-scan, forward scan and down-looking sonars, both single- and multi-beam. We explore the meanings and implications of holiday zones, spatial sampling restrictions, vehicle motion, reverberation, side lobes, transmission loss, target specularity, noise figure, bandwidth, display dynamic range, adaptive gain control, image registration and slant range correction, and their effects on sonar performance. A number of user-oriented concepts and quantitative measures of goodness are introduced and described, including area coverage rate, information density, and a novel figure of merit that combines both of these in a single number. Tabularized data for several commercial sonars are presented, including a new, high performance side-looking unit recently developed by Sonatech, Inc.