Several of us have played this nice Jürgen Strohm game and have come to the conclusion that the three tech tracks are not equal in their value. This leads to a single strategy, pollution tech.
So, we use this variant...
1. Tech tracks cost 3, 4 and 5 euros to develop. 3 for worker, 4 for materials, and 5 for pollution.
We also play with the variant posted in this forum...
2. When auctioning raw materials, you may put from (lowest developed material track) to (highest developed material track). e.g. If one player has reduced their raw material track from 5 to 3, the least number of goods that can be offered is 3. The doubling card still doubles this number.
I'm sure some will disagree, but I've played the game several time with and without these variants and I think that it is a better game for it.