Having had both, I'm very partial to the Streamlight aluminium, much larger and tactile switch, can be used in sub-freezing tempuratures with gloved hands, unlike the Maglite (granted years ago and may have changed). Never saw a failure with a Streamlight switch, many with the Maglites, also a rain entry point. Always found the beam of the Streamlights superior to the the Mags.
As mentioned, many departments prohibt the large cell metal lights, seen by many administrators as a metal bat (some went to plastic version), and the current generation LED CR123a battery are nearly as bright, some even brighter, than the big bats, take up obviously take up less space and weigh less. That said, there is nothing as enjoyable as a large metal flashlight to push open, lift up, as an extension of one's arm, and provide blinding light when needed.
Being right handed, I always hold a flashlight with my left, with the larger light, tailcap end rested on the shoulder, while the hand was at the neck taper, allowing for easy switch manipulation, and with the flick of the wrist, bringing the end forward to use as a push pole or baton strike.
30 years of nights found that all lights will fail or get dislodged at the worst moment, so I've carried three lights, all on the left, primary in hand (largest), secondary on belt with a tatical switch, bezel down, and a third, small backup flashlight (now an E1b) with assist blade in the left front pocket.