Searching an optimal sequence for a given set of characteristics (say, Strength and Speed) is a constrained linear bin packing problem. So it's solvable, but it's NP-hard. Which makes optimizing your sequence either a mater of feeling or of luck. Clever, or annoying ? Can't say.
Nonetheless, I too figured out that REP/STR/DEF is unbeatable. Having two cells means creating units at twice the REP rate, so the more cells you conquer, the (way, way) more REP comes in handy, without you having to do anything.
To conquer cells, you need STR or SPE (or AGI). It just so happens that given the gene pool it's easier to combine STR with the rest. Then you want to keep your cells to REP, so you get DEF.
Excellent game, but a lot easier than the first if I remember correctly. Phage Wars 3 will need to bring on challenge !
 "Idle Mine"){kind=icon}
 "Phage Wars 2"){kind=icon}
 "Hexcelle"){kind=icon}
 "20 parts apart"){kind=icon}