Typically (but not always), you get maximum value when you earn the "native" points. For example, on a $300 Marriott stay, I would rather have the 4500 points than 1 SW credit. Obviously since the 1 SW credit is fixed and the MR points are per-dollar, there is a breakeven point on a cheap one-night stay where you might want the SW credit.

Hertz is trickier because ZE1 points have great value to some but little value to others. If you ever have a need for 1-day standalone rentals, the ZE1 points are valuable in that 600 pts = 1 free day with no strings attached. Again, I think Hertz SW awards are fixed, ZE1 is per dollar, so on a cheap rental you have a decision to make. (And triple credits is a pretty nice deal!)

I almost always choose to earn the "native" points to maximize the value I get. The exceptions are promotional offers (e.g., 5000 AA miles for 1 night Sheraton stay) or cases where a fixed partner earning is more valuable than a per-dollar native-point award.