In Spades, what to lead from {Ace,King,...}
Spades and Contract Bridge share most of the same mechanics as far as play of the cards are concerned, and this has long been a matter of disagreement between experts. Also, the style of playing from AKx bears on what is appropriate from lower touching honours.

Three main styles have developed in Bridge:


Traditional:


Highest from touching honours at the top of the holding, except K from AKx, so: K from AKx, Q from KQx, etc.; but highest if the holding is a doubleton.
Highest from an interior sequence, so: Q from AQJx, J from KJTx, etc.
Advantage:
The play of an A can be made without the K, as from Ax, without misleading partner.
Disadvantage:
Additional ambiguity on the lead of the K, which can be from AKx, KQx, or Kx

Traditional - with A from AK


As above - but with the the play of A or K from AK and AKx holdings reversed. Partnerships must agree if this is played throughout the hand (rare), or just on Opening Lead (much more common). In the Trump suit (always Spades in Spades, of course) the K is lead from AKx because the lead of A from Ax is more common.
Disadvantages:
(i) The play of an A potentially misleads partner due to the ambiguity between Ax and AKx holdings.
(ii) More complex than vanilla Traditional because of the exceptions.
Advantage:
Reduces ambiguity on the lead of the K, which can now only be from KQx, or Kx.

Rusinow:


Second highest from touching all honours, so K from AKx, Q from KQx, J from QJx, etc.
Highest when the touching honours are an original doubleton.
Second highest also form an interior sequence, so J from AQJx, T from KJTx, 9 from QT9x.
Typically played only on the opening lead - Traditional is played on all subsequent tricks.
Disadvantage:
More complicated than either of the first two, due to being an Opening Lead convention only.



Of course, it is paramount that you and partner be in agreement on which system will be played. That experts have no consensus between the three systems suggests that the differences are relatively minor.

There are any number of Contract Bridge sites that discuss both Opening Leads and other defensive agreements of partnership benefit, such as Richard Pavlicek's site.