I have 3 very similar planets:
Average Very-Rich
Large Rich
Very Large Extremely Abundant

By the numbers these are within a point of each other for production. On one hand the smaller planet has a greater multiplier so the same number of mines will get more results for less cash investment. On the other hand the larger planet can pack more defenses with less effect on overall production.

Which is more important to you? Defense or Efficiency? Which planet would you choose?

Sean

I would choose none. It heavily depends what stat you are talking about.
I'll look for the following (artifact/mining):
Vlarge Very Rich
Large Extremely Rich
Average I would avoid unless it has Extremely rich, but still not the first few choices.

IF you are talking about research, I'll take only massives/very massives.

Well in this case I was thinking Mining. I'm level 31 and have 40+ planets to choose from but everything rated higher then this is either owned by myself already or owned by an enemy. It will take me far more time and resources to try to capture a planet and then I would need to spend more space defending it. I'm staffing up for another scan blitz but the least one was less then useful. A lot of tiny sparse moons. It didn't leave me a great selection to choose from.

Now if you had a planet you wanted to lend me instead.

Sean

Well, among them all, the average will produce more resources assuming all space for resources. But I think it is always better to go for the largest. A Vlarge will allow better customisation when the time comes.