Choosing a new boiler. Dunkirk or Weil McClain ?

Replacing a 17 year old HB Smith boiler. Old boiler was 4 section, we are downsizing to 3 sections..
We've narrowed the choice down to 2 quotes (out of 4 quotes). A Weil McClain WTGO-3 or for about $350 more a Dunkirk Ultimate Cast Iron Model PFO3T... Both would have tankless water heater.
Both would use a Beckett model AFG burner.
Any info on these boilers or boiler replacement in general would be greatly appreciated.
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