Paraboloids (parabolas spun around the axis to make a doubly-curved surface) require continuous aiming. They make a very hot point focus, which can approach the temperature of the surface of the sun.
Parabolic cylinders (a parabola swept along a third dimension to make a singly-curved surface) only require aiming according to the season. They make a moderately hot line focus. Tracking the sun in only one dimension also gives you cosine-law power loss, as with a non-tracking photovoltaic panel).
Both collect heat in proportion to the area of sunlight intercepted. (You can terminate the trough with mirrors to fold back the light that would have ended up off-the-end and bring it back to the focus pipe.) The dish is more efficient than the cylinder because it can collect it at a higher temperature. But the cylinder is easier to make big, to collect more heat.
In addition to being easy to aim, cylinders are easy to construct: Take moderately stiff mirror material and bend it, holding it in shape with forms. Or cut up mirrors into strips narrower than your collection pipe and aling them on supports. Unlike a dish, you can make a cylinder as long as you want.
Seasonally-tracking parabolic cylinders, even at reasonably high latitudes, are adequate to produce "process steam" - boiling water and bringing the steam up to a reasonable temperature but not strongly superheated. This is quite adequate to run a steam engine (or cause a steam explosion if mishandled.) One potato processing company (in Idaho, I think) was in the news a couple decades back because they installed long parabolic cylinder solar collectors on their plant to make process steam that they in turn used to heat oil for precooking their french fries.
The collector can be a black-painted iron pipe. Putting it inside a glass cylinder improves the collection by limiting conduction losses to the air and reflecting re-radiated far infrared back at the pipe. Covering the trough with glass or plastic will keep the dirt off the reflector.
Aiming the reflector according to the season can be done by pivoting it around the pipe and (to a lesser extent) by moving the pipe.
