In your 250, I would use a multi-viscosity oil, like 10W-40. That is what I used in everything, until I had a chat with the fellow who is rebuilding my 235. He convinced me that the 235 was designed for a straight weight oil, not a multi-viscosity. So, when I get it back, it will be SAE 30 only.
As far as brands, I and my dad have used TropArtic for years, and have had very good results with it. Personally, I would stay away from Pennzoil or Quaker State. They are parrafin based oils, and I understand that they tend to attract quite a lot of moisture.
