When using "best execution", I've never had a stop blown through or ignored. BUT I always get lousy stop activation when trading Nasdaq. Everytime single time I am watching, the stop is activated a good minute or so AFTER the ASK price matches my stop. I've simply NEVER gotten filled on a Nasdaq stop at a reasonable price.
What I do now is purposely set my stop above where I would normally set it, in two stages. So say I want a stop at 50.00. First, I figure the BID/ASK spread is about 2 or 3 cents. So I make it 5 just to be sure. So the stop is 50.05 at this point. Second, I know that because IBs stop election software sucks, my stop will really get activated at 49.97 or something in that area.
So I set the stop at 50.13. This way, after the stop takes its minute and a half, and I get my lousy fill, it will be in the ballpark area of what I was looking for in the first place, which was around 50.
In short, IB has a real problem with Nasdaq stops. NYSE are fine.
Wet