I like speed runs. I tend to get more legendaries as rewards for completing the strike. Not many legendaries drop inside. Plus you get the Rep and marks. It's more efficient to complete 10 strikes in 2.5 hours rather than 5 strikes in 2.5 hours killing more trash mobs. Double the Rep, double the marks, and in my experience more rewards to boot. I've received exotics as a strike completion rewards, and again most my purple engrams come from completing the strike, not as a trash drop. (or as a Rep reward from levelling my faction again) So really, speed runs do make more sense.