Tech

Depending on which stage you are and whether you are playing campaigns or conquests. For conquests most important is aircraft 5 to get motorized infantry in paratroopers. For campaigns it is not so important. Than for axis/allies campaigns most importan is artillery after it infantry, for 39/43 conquests first infantry, than artillery. When you reacn NATO/WTO campaigns and 50/60 conquests, most of all you need tanks and also nukes level 2 (higher level bombs are quite expensive and not worth it for that time). Improving some rockets is not so bad too. Supply, ships and antiair is not so worth to upgrade, this you can just do when needed and when you have free resources or when any campaign or challenge requires that. Forts are not worth to upgrade at all. Space is just for fun and ion cannon is too expensive (just first level to have it is worth, than to get significantly better effect you have to pay too much medals, so it can be done only when you have good academy gens and ECs). When you reach aliens, you will need everything: infantry, artillery, tanks, missiles, nukes, only aircraft not more than level 7 in order not to loose motorized infantry paratroopers.