The hard part about purchasing a unit is sifting through the BS. .
You better have a thick skin if you want to hang in the wood boiler world.
Ideally, if the following are true:
1. You can power vent your oil burner and have it meet code (distances to windows/doors, not dumping on a deck/patio, etc).
2. You don't mind losing a piece of your basement to 1000 gallons of water storage.
I would definitely go with a standalone wood boiler designed to operate WITH storage.
If NEITHER of those is true and you WANT a combination boiler and one that can be run without storage, you really only have one choice left and I'm not even going to bother to say it since Fred and Mike are already in here.
ac