In my opinion, they both have a purpose.
The loaders are usually a quicker reload. They fit neatly in a coat pocket, center console or backpack pocket and can get banged up a bit.
Speed strips allow for partial reloads, are flatter and can fit into pants pockets. They also fit neatly in some "watch pockets" on pants. They also fit nicely in i-pod cases. They also fit nicely in a sun visor "map" strap in a car. They also fit nicely in...you get the point...You need to be a bit more careful with where you put them, lest a bullet get dislodged on the way out of said pocket.
That said, they both require a fair amount of practice to be somewhat quick with them.