When comparing OpenGameArt vs GameDev Market, 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 GameDev Market is ranked 6th. 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 Offers a good variety of resource types
GameDev Market includes 2D, 3D, UI, and audio resources.
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 Personal storefronts could have better discoverability
Currently personal storefronts / seller profiles have a simple list of assets. There are no categories, tags, genre-information, type information, etc that could help narrow the list down.
Con Basic search
Search only matches keywords with titles. No way to search based on type, color, etc.