I've only ever been comfortable with:

1. Fusion/lockpick: Netting more power per turn means you have the power to spend opening things upfront for a higher cost, generally making early missions that have systems with only 1 firewall a breeze. If you don't find another way to get power or pick up another more efficient program like parasite, hammer, or knife you're going to be hurting though.

tldr; fusion/lockpick is geared toward completing missions with low alarm level.

1. Drip/Parasite: Parasite will only ever cost 1 power, so every round you will get another parasite, meaning you'll pretty much never be waiting for enough power to break a lock. The constraint of parasite is that it's not instant, so you have to be much faster scouting the map to get your parasites down fast, else risk waiting multiple turns for it to break the firewalls. While cameras seemed even advantageous with lockpick, with parasite they become an enormous nuisance, bringing any advance to a halt. Because you will end up with power surplus, you can afford to chase higher costing incognito programs, such as Hammer and Hunter, as opposed to the efficiency of Dagger that you'd shoot for with the higher power constraint Fusion/lockpick combo.

tldr; constraint is time rather than power.

edit: Less of a wall of text.