Most of the time collectors are preferred over reactors. A single reactor generates roughly the same amount of power as three collectors, but requires 10 more energy to build. By comparison, three collectors built in series would take ~8.3 seconds less time to complete and would generate an additional ~5.0 energy before the reactor would be constructed (not accounting for the path length).
Yep, the shorter path definitely helps. But I generally switch over to reactors once I'm generating energy faster than I can use it to build collectors (you don't want to have excess/unused energy).
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