I find it interesting that folks pan the C frame presses as inferior to O frame presses, but both the Forster Co-Ax and Redding UltraMag are C framed presses, and widely deemed among the best presses available. Both of these anchor the linkage to the top of the press, very near the die, for maximum stiffness and strength.
There are some features of single stage presses that make one easier to use than another. Such features include how well they handle the spent primers and debris, keeping them off the bench and floor. The best presses for this have a hollow ram or tube that captures the primers and directs them to a catch bottle, bucket, etc. below the press. Adjustable handles (length and/or angle) allow you to fine tune the stroke length of the handle stroke for the leverage the task allows. Some folks (like me) prefer tubular gripped handles, but others prefer ball-end handles. Some presses incorporate, or are compatible with, quick change die features. All of these features have varying value to different users. And of course, they come at different price points too.
There are four popular single stage presses that seem to stand out in value and performance, with the above features in mind: The Lee Classic Cast, the Redding Big Boss II or Ultramag, and the Forster Co-Ax (what I use).
Andy