Well, it seems like we've gotten pretty much everyone to agree that upgraded Harvesters are an order of magnitude better than upgraded Econ Stations, which is a start.
Not in all games, especially those which have middle-level counts of human controlled systems.
Harvesters get their early-game boost primarily because of the extreme resource point count on the human Homeworld. However, once you have enough space to build your Econ IIIs, they outweigh the harvester income pretty solidly, up to the 10-15 system count. After that (because you can't build more Econ IIIs) the harvesters take over again, and become the better choice.
No matter what numbers you come up with for harvester/Econ income values, this trend will always hold true. Harvesters better when you can't build Econ IIIs, Econ IIIs better when you can.
Just as a reference, here's the thread we had last time the economy question was debated:
http://www.arcengames.com/forums/index.php/topic,10169.0.htmlHang on, a full cap of your mark Is before the first wave?
Very early game economy may be a bit strong with harvester upgrades, but it's never been that strong for me. It is usually around the 3rd or 4th wave where I can finally build to cap.
I usually upgrade to Harvester IIIs during the first second of the game, and usually complete a full cap of Mk I fleetships + some turrets about the time the first wave arrives. Against some AI types (Spire Hammer, Starfleet Command, Heroic) this is pretty essential. If the initial economy is nerfed hard, then these AI types can become impossible at high difficulty levels.