In my opinion, there is no such thing as a general avoid note. It is funny, I got the same question about a week ago and posted a reply on my "Infinite Guitar" Blog. I'll give you a brief explanation, but if you want to read the detailed answer, go here:
http://theinfiniteguitar.blogspot.co...oid-notes.html
You are correct to assume that the lydian mode is sometimes preferable because the #4 doesn't rub against the major 3rd in the chord. I like to think of the scale as better balanced. But, what if your chord was a sus chord? then the #4th would be plain wrong.