I've used both books and have liked both. After Thomson's takeover, they seemed to branch out into books on bookkeeping and other topics as well as taking topics out of their core books to create new books such as on depreciation. Since that time, I've tried Kleinrock's Quick Answers and The Tax Book in a couple of formats.
I like The Tax Book cites. Just opened to any page, it's Interest Paid -- Itemized Deductions. It starts with Cross References listing such things as the instructions for Schedule A, Form 1098, and Form 4952, and IRS Pubs 535, 550, and 936 giving their full titles too, and IRC section 163. Next are Related Topics giving things like Student loan interest deduction on Tab 12 as well as three others. If I need more than the quick answers, examples, court cases, planning tips, and author's comment, I now know where to look for IRS guidance from the Cross References list. One year I bought the CD; then I just clicked on a Cross Reference to go straight there.
I was used to how to find things in Quickfinders, but I found fewer and fewer answers, examples, commentary, etc., on the issues I encounter as the years went by. I loved the chart they had comparing pension plans. It was designed by TTB authors while they were QF employees, so the copyright belongs to Thomson; and it'll never appear in TTB! Over time, TTB has become more useful to me for quick answers as well as a starting point for research.