The databases do not differ much on their coverage of the primary sources. What sets them apart is the quality of their editorial content, the way they organize their information, and their web interfaces. In a commercial setting, pricing is also a key consideration.
Each of the tax research databases described below integrate all the primary sources for federal tax law with the publisher's secondary sources. As general legal research tools, LexisNexis and Westlaw provide access to these sources, but it is usually better to use one of the specialized tax research databases because they have unique features to make the tax research process more efficient. For example, these databases allow the user to navigate efficiently between the full text of primary source documents such as the Internal Revenue Code sections, regulations, IRS rulings, and the publisher's secondary sources including editorial explanations and annotations.
BNA Tax and Accounting Center includes all primary sources plus BNA's Tax Management Portfolios, including the U.S. Income Portfolios, Estates, Gifts and Trusts Portfolios, Tax Practice Series. It also includes the Daily Tax Report, the Weekly Report, and various tax journals. It is organized by subject and geared toward practitioners.
Thomson Reuters Checkpoint includes all primary sources plus key secondary sources, including the Federal Tax Handbook, Federal Tax Coordinator 2d, the United States Tax Reporter, and two WG&L treatises (in our subscription).
Tax Analysts includes detailed federal tax news in Tax Notes Today and the Exempt Org. Tax Review. You have to register at the link below for an account using your illinois.edu email to use this database, but the blog is free.