Interesting, I always thought modified accrual, for plan purposes, was simply cash basis for everything except accrual basis for contributions. I guess that's what the more complicated description above boils down to.
Anyway, we almost always use that (modified accrual). The benefit is that your plan tax return contribution ties in with your business return deduction, and it provides an aid in reconciling. The downside is that it takes longer to complete since the contribution may not be known for many months. It seems that the large bundled service providers tend to use cash, since in theory you can push a button on Jan 1 and complete the financials and not have the messiness of waiting for contributions to be determined.