Productivity is most important by engineering management rules, but enjoyment is most important for engineers. One stems from the other.
Rob PikeRule 1. You can't tell where a program is going to spend its time. Bottlenecks occur in surprising places, so don't try to second guess and put in a speed hack until you've proven that's where the bottleneck is
Rob PikeData dominates. If you've chosen the right data structures and organized things well, the algorithms will almost always be self-evident. Data structures, not algorithms, are central to programming.
Rob Pike