Don't use the lowest grade gas either and that helps with what ever mix. I think the best is Opti2 fuel mix. I burn the mid and high octane fuels. As far as the fuel and oil caps I haven't had any problem with them at all. I don't have the 250 model 044, 026 and 046. The rest of them are Husky's.
Save yourself a little money and just buy the higher octane gas. Only buy enough that you don't let the jug sit more than a year. I have used my saws with the Opti2 that have sat for a year with no problem. Generally I run them out of fuel when I can. It is a mess trying to pour the fuel back into the gas jug. Any good fuel stabilizer helps.
I agree on the higher octance gas as well.
I just bought a MS250 yesterday and the manual says minimum 89 octane (midgrade) as recommended minimum.
This is a double-edged sword.
87 Octane outsells 89 and 93 combined by about a 10:1 ratio. When you buy higher octane fuels, it has a little longer of a shelf life before the octane has faded down to where it's "too low" to be useful. So, if you're buying 93 Octane, and it's been sitting in the tank at the station, it won't give you much more time before it, too, has degraded to the point where it doesn't meet the standards of the engine you're trying to run it in.
When you go to fill your 5 gallon can, add a high-quality stabilizer that's MEANT for ethanol-containing fuels. Always fill your gas can at the same time every month and just before you fill again, empty what's left into the tank of your car. That way, you will always have fresh fuel on hand for the small engines.
Don't leave gas in the carbeurators of your small engine equipment - close the fuel line (or empty the tank, like the saw manual states) and then run it until it dies - this keeps the gas from varnishing the carbs. When you mix fuel and oil, mix the smallest quantity that you can while keeping ratios correct. And, be sure to spread that fuel around through the different two cycle equipment to use it up.
As for the 250 - I just bought one myself to use for smaller work. My 290 is a much beefier saw (it's in the moderate use category and the 250 is in the light use category), but it's not something I like to be tossing around a lot when limbing or doing smaller work.