1. Which work the best? If you are new to PH's, then stick to the basics. 1AD/4AD and 1T/4AD are very popular. Once you've had several (3+) cycles under your belt, then other PH's may be used. M1T, though very popular, is also very dangerous. I feel that the risks outweigh the rewards. For the basic cycle, 6OXO will suffice for PCT. Once you get into the methylated and stronger PH's, then Nolva/Clomid would be wise decisions
2. How effective are they? Bewaring a solid diet, exercise, rest and planning, they can be very effective. HOWEVER, everybody reacts differently, so don't rely on what I say as though it is the standard.
3. Do they have any effect on mental accuity like regular testosterone? They can have a minor effect, though I'm not too sure. I rely on nootropics for this. Sorry, I do not know
4. Which are legal/illegal in California. As of right now, there are a few that are currently illegal to purchase in CA. I am unfamiliar with the list. I suggest you contact vendors/retailers to find out.