Brand doesn't matter. As mentioned, be sure to flush it out with clean water at the end of season.
I have never had the cheap stuff gum up a fogger. Only difference might be the density of the fog when it comes to cheap vs. expensive. As for the water to flush it, your not running more than a few seconds of clean water thru the system, not much chance of getting any deposits. This is a topic that I'm sure will have a wide variety of opinions. Bottom line is, do what works best for you.I disagree, the cheap stuff will gum up a fogger much faster then quality juice, and I wouldnt recommend using just water to clean it out, at least not on a quality fogger, I guess you could use the cheap stuff in the $50 Spirit foggers or ones like them, water has impurities that will collect on the different internal parts and cause issues, mostly the nozzle.....I suggest purified water or distilled water, or fog machine cleaner if you want to spend the money on it.