Question for maintainers of popular open source projects: Would you prefer two days of developer time/month, or a comparable cash donation?

Charitable organizations often prefer the cash [1], but open source is different -- I suspect many developers have more context and preparation than the typical volunteer. On the other hand few people will be as efficient in a code base as the original authors.

[1] (http://www.theguardian.com/voluntary-sector-network/2014/mar...)