There are many excellent dental cements dentist can choose to use.

That depends on what the crown is made of, the shape of the prepared tooth, the patient's decay rate...
Your dentist should be able to recommend the best cement. Resin cements are very common. Resin Modified Glass Ionomer cements are also useful. These are probably the most common.

There is no one best permanent dental cement. There are different ones for different applications. A dentist makes the decision according to their experience and the type of restoration being placed.

Nothing is permanent...we have temporary or definitive cements. THE ADA recommends 5 year longevity

There are many very fine "permanent" cements. The most widely used these days are called Resin Modified Glass Ionomer or full Resin cements. There is not best among these choices.