The speed loader is clearly faster.
The speed strip is flatter and (in my experience) more likely to actually be carried and, with practice, is faster and surer than loose rounds.
In either case, practice under stress (timed fire, buddy yelling in your ear or throwing tennis balls at you, Jeopardy theme playing in the background) will give you a faint idea of how likely you are to fumble in the situation you seem to be addressing: a reload under fire.
In the days when revolvers ruled in law enforcement, as soon as speed loaders were available an authorized, I switched from speed strips in dump pouches. But for concealed carry the speed strips still had a role - after you have taken the time to hide your weapon, a double speed loader pouch on the belt is a little on the nose.
Bottom line: the speed strip in your pocket is always a faster reload than the speed loader you left at home.