Baseline Selling covers four points in the evolution of an opportunity within the selling process: first base (suspect), second base (prospect), third base (qualified) and home (closable). SPIN is a questioning process that can be mapped onto Baseline Selling and the entire process takes place between first and second base. Most of the concepts in Strategic Selling take place in the on-deck circle and between second base and third base. So, while neither of them are complete processes, both qualify as methodologies or approaches.
The 2nd topic we can explore is how applicable they are to your business. As good as SPIN is, most salespeople simply can't replicate it. It's just too difficult. So Baseline Selling has a simple questioning process that anyone can do - right out of the book! As good as Strategic Selling is, it isn't tactical. In other words, it's a book on strategy but it doesn't explain with detailed examples of dialog how to execute the strategy. Baseline Selling takes only a few pages to explain the four steps and the remaining 213 pages are devoted to tactics - how to get around the bases. Is Baseline Selling for you? Most sales development experts think so!
[Updated - This short video shows a much better comparison of SPIN, Solution Selling and the Challenger to Baseline Selling]