I wouldn't class myself as savvy... but I'll have a crack at...

I wouldn't class myself as savvy... but I'll have a crack at answering your question (or at least providing you with some insight into how I make my decision).

- Historically (this is from my memory, but pretty sure the data backs it up) the SP has been lower than the DRP price at/around the time of the dividend payment. Buying on-market has been possible at a lower rate for recent dividends (not a prediction for the future).
- DRP has no fees (so the smaller the income, the more incentive to go with DRP as there is no brokerage)
- DRP can be 'set and forget'. You don't have to watch the market to get the right buy-in price
- DRP may have tax implications (in regards to cash-flow). If you are on a personal tax rate above 30% you will need to pay tax on the dividend (regardless of whether it is cash or DRP). If it is substantial enough you will have a large out-of-pocket expense but no cash incoming (because it is all re-invested).