Energy Logic is by far the best for the money. They have a much better design than Clean Burn and Reznor uses a gas-fired boiler vessel with a waste oil burner. It does not work well and has to be cleaned a lot!
Energy Logic is the best brand to burn vegetable oil. Vegetable oil can granulate if it gets cold and cause plugging in the system. Energy Logic offers several things to help with this. Energy Logic can burn a broader range of oils than any other brand.
From personal experience, the Clean Burn brand is a good brand, but Energy Logic offers better, longer lasting heaters. They cost less to maintain, are easier to clean, and are very cost competitive. Check it out before you buy again.