I have built a skimmer with a round body with a square base and it worked well (I still have it but it is out of service for the time being). I am collecting parts to build several cone skimmers too. Cone skimmers gained popularity/desirability for a while. Manufacturers liked them because hobbyists couldn't replicate them easily. Hobbyists liked them because they look cool. They do have an advantage in that the cone directs the bubbles to the collection cup. But you can work with any shape to do that.
After messing around with many skimmer designs (including turning a Sea Clone into a decent skimmer), I have found that the secrets to a great skimmer is the following:
-It should be recirculating. The recirculating pump should have a needle wheel impeller.
-If it is not recirculating, the feed pump should have a needle wheel impeller (or any bubble chopping design).
-The water column/bubble column should be adjustable. This is normally done with a water flow valve on the output of the skimmer.
-It should have an air control valve. This also helps control the bubble column, and bubble quality. It also controls the skimmate quality.
-The collection cup should be self draining to a separate collection container. If an event causes the skimmer to produce wet skimmate, it often will cause the collection cup to overflow.
-If the bubble column needs help reaching the collection cup, an air pump with an air stone in the skimmer will work wonders.
(It's going on midnight and my brain has already gone to bed. I may add to the list later.)