Hello Stratton. I've only run 2 boilers myself but familiar with a bunch that friends and family have. Various brands and sizes.
Pros and cons of my own boilers are probably covered in detail in past posts. But here are highlites
Nature's comfort GT 220:
pros- large firebox, simple firebrick (after upgrades), minimal smoke
cons- stupid screw drive actuator motor for draft door, cheesey door latches, high exhaust temps, one supply and one return port
Optimizer 250:
pros- nice fit and finish, nice door latches, low exhaust gas temps, easy to clean, minimal smoke, 2 supply and return ports
cons- nozzle (wear item), expensive up front cost