Hi Steve, good question. For the rectangular ones, they come in a number of sizes as well so knowing the distance that your burners cover from front to back is important. There will likely be some hot/cold spot issues, some have put both burners on a medium heat and let the iron get pre-heated well, others put the griddle in the oven to get a consistent temperature before starting.
Depends too on how many you're feeding. You can still turn out a fair number at a decent pace with a round griddle, just put your oven on at 170 to hold the extra cakes until you're done cooking the rest.
