For the Governor's abilities, consider this: Remodel costs $4, but could get to $5 if you had an extra action. +3 cards/+1 action doesn't exist, but would be a beast and would cost about $8. There is also nothing that lets you gain Gold straight up because it would be very expensive. So, the last 2 are pretty insane abilities
Now, consider what the other guy gets. He can get an upgrade if you remodel. That costs $5. Or, if you draw cards, he just played a Lab. That also costs $5. But if you gain gold, he gets a Silver. How else could he get that? Well, with Squire (from Dark Ages) he could gain a Silver, but he also has a choice, and generally choices are better than the straight up ability. Also, Squire gives him +$1 while he's at it. And how much does Squire cost? $2. And when you play Governor, he doesn't decrease his hand, like he did by playing Squire. So, gaining Silver is quite likely the worst gift that Governor gives, and since cards and gold are similar benefit for you, gaining Gold is in general the best play.
Of course, there are always edge cases. For instance, Governor/Goons, where if you know you can play the Goons there's very little penalty to playing Governor's draw. And, in a Goons engine you probably don't want the Gold that much. But, that's situational. With all three considered in a vacuum, gaining Gold is on average the best.