When comparing OpenGameArt vs Freesound, the Slant community recommends OpenGameArt for most people. In the question“What are the best sources of royalty free game assets?” OpenGameArt is ranked 3rd while Freesound is ranked 5th. The most important reason people chose OpenGameArt is:
All assets made available through OpenGameArt must be licensed under one (or more) of the following: CC0, [OGA-BY](http://opengameart.org/content/oga-by-30-faq), CC-BY, CC-BY-SA, GPL or LGPL.
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Pros
Pro Committed to free/open licensing
All assets made available through OpenGameArt must be licensed under one (or more) of the following: CC0, OGA-BY, CC-BY, CC-BY-SA, GPL or LGPL.
Pro 2D and 3D art
OpenGameArt has both 2D and 3D art assets.
Pro Big library of varied CC0 assets
OGA currently has an impressive library of free assets, especially in the texture department.
Pro Supports asset requests
OpenGameArt has community forum sections dedicated to Resource Requests and Open Commissions.
Pro Creative Commons licensing
All assets made available through Freesound are required to be licensed under either CC0, CC-BY or CC-BY-NC.
Pro Extensive asset information
Each sample has a details page which includes a waveform view, a full-length audio preview, user-assigned tags, author-assigned "pack" grouping, and an author chain ("remixes and sources") for derivative assets.
Cons
Con Mediocre organization and search functionality
The curator of OpenGameArt acknowledges that the tools for finding the assets you need are sub-par. Correcting this is a near-future priority for improvement, and as of September 2014 is the next milestone goal of the site's Patreon campaign.
Con Assets may have restrictive licenses
OpenGameArt hosts art under any of several licenses, some of which may not be suitable for commercial projects or for release on certain distribution platforms. Careful review of which licenses are compatible with your project is essential. The site's search facility allows filtering by license.
Con Some assets may have restrictive licenses
Freesound permits uploaders to select the CC-BY license, which disallows the use of DRM, and the CC-BY-NC license, which disallows commercial use entirely. Licenses are prominently displayed on an asset's details page, and represented by a small icon in list views, but there is no option to filter by asset when searching or browsing.
Con Audio samples and sound effects only
Freesound does not host any kind of non-audio asset.
Choice of music is also scant.