Several things to consider up front. First, what, if any, regulations does your state have in place? That may dictate the type of burner you must get (ie. gasification). Second, if regs don't limit your choice, then do you want to burn any/all wood or only seasoned wood? You need seasoned wood for the gasification units to work properly. You can burn larger logs and unseasoned wood in a basic/standard boiler. Third, do you want a basic damper or fan operated air intake? Fourth, standard or dual fuel?
I have a Central Boiler Classic 6048
Central Boiler - Outdoor Wood Furnaces I'm in my 9th season with it. I love it. 4 guys have bought the 6048 after seeing mine operate. 1 guy went with a different company for the fan operated air intake.
If I replaced mine I'd strongly consider the Portage and Main Gasification unit.
Wood Gasification Water Furnaces | Boilers I'd struggle with the decision, but would probably stick with the Central Boiler unit because I like being able to burn large logs and don't want to worry about moisture content. I can burn anything in my boiler. It can be dry or dripping wet or covered in snow and ice. If it fits through the door opening, then I burn it. With a gasification unit I would have to burn smaller logs that were split and seasoned and stored under cover. My wood sits outside, uncovered. I can cut a live tree and start burning it right away; no waiting for it to season.
Lots to consider. Buy the best you can afford and don't skimp. Do it right and do it once. You will recoup your investment many times over.