Which means of spying have you used that have been usable in court? Which ones to judges just throw out?

You need to explain this question a bit more.

Why would you need to discuss spying in court? When people divorce for adultery, they can usually provide evidence without having to discuss how they got it.

Are you facing court over this issue?

Welcome to MB.

Photographic evidence is usually best. Once viewed by the court, even if the question of the legality of obtaining them is raised, the photos have the tendency to "poison the well," so to speak.

Disclaimer: I am not a lawyer. And my lawyer told me officially that she was not recommending that I photograph incriminating text messages from my WxW's cell phone...

We had photographic evidence as well as video surveillance evidence from my PI. We also got court documents supporting what "might" have been going on in OW's apartment she had shared (before shacking up with my xwh) and we subpoenae'd the OW AND HER EX ROOM MATE.

We got more evidence than you could shake a stick at. The mother load. Found out the OW AND HER ROOMMMATE did DRUGS TOGETHER on more than one occasion and her friend testified to that under oath in court.

Anyhow, in many states, voice activated records ARE ADMISSABLE as long as one of the two parties involved HAS KNOWLEDGE of the conversation being taped. In some states, it's where both have to have knowledge. But it can be used as a "tool" along with some other evidence like photo or video (usually always admissable) to push the ws over the edge and admit everything.