I read the instructions as stating that you can place an action and/ or a money and/ or a property. But others say you can do any combination of the three in any of the three piles.
The three cards can be any combination of properties, actions, and/or money. From the rules (abbreviated for clarity):
PLAY UP TO 3 CARDS from your hand, onto the table in front of you. You don't have to play any cards if you don't want to. Play your 3 cards in any combination of the following: A, B, and/or C.
A: Put Money/Bank cards into your own Bank
B: Put down Properties into your own collection
C: Play Action cards into the center
You can play any three cards from your hand during your turn. These three cards are not otherwise restricted in type; you can for example,
Play three Deal Breaker cards and potentially win the game
Play three Pass Go cards to draw a total of six new cards
Lay down three properties to either form a set (and possibly win the game immediately) or to complete existing partial sets
Play three Rent cards, either using different properties/sets or the same property/set as the base
Lay down three Money cards in your bank
You can also choose to end your turn before playing any cards at all, let alone all three cards allowed.