I see people claiming that a single solution solved all spam issues, but in reality each solution has different tradeoffs. Web of Trust has lots of collateral damage. You filter out legitimate posts from people completely outside your circles. I would hate to lose that.
The best anti spam will likely be a combination of anti spam algos and WoT, allowing people outside your circles if the message doesn’t trigger your spam algo.
Lightning is effective as well, but not everyone uses that.
What I have been thinking about and will most likely be moving towards is a pluggable nostrscript that takes various values as input (WoT score, the note, total zaps received from that user) and provides it to a pluggable spam filter so it can be constantly updated to fight new spam tactics.