We bought one composter and liked it so much we purchased another one the following year.  It has a large opening that ensures it is easy to get the compost materials in and out of the container.  It is large enough for the contents to heat up but still small enough to turn easily. Living in a high-altitude, zone 3 area (aka. cold), we are usually able to empty 3 of our compost barrels in the fall and the fourth in the spring.  An added bonus is that this composter doesn't attract rodents.