my opinion is that AP's are better for smaller ships where ecm may be overkill.
For example:
Advanced projectors on a cr90 is really fun. it essentially makes it able to take 11 damage before it dies.
as not many large ships concentrate down on a single cr90 there is a better chance that it will be able to use its redirect.
conversely large ships tend to do better with ecm because smaller ships WILL concentrate fire against them en mass every time the opportunity arises,
Personally i use AP's on my mc80s as the redundant redirects make it very difficult to block both AND the brace.
