MathMad Well, there can be different approaches to this problem.
The overall consensus seems to be go for the most powerful regen items, even if it means less items in total. The idea behind this is to maximize your "per column" regen speed, rather than overall regen speed.
So for example for Egypt, using this approach, you should get 1x Most powerful regen item and 1x second best regen item, which in the case of this event is:
The other option would be to get
As you can see, in the 2nd option you end up with a higher overall regeneration speed, but instead of having 1 top item, you get two second-best ones. The decision is yours, but like I said, if you're planning to stick with the game for a long time, taking less but more powerful is probably better in the long run.