No. Standard (American Edition) Monopoly game board layout. Mediterranean and Baltic Avenue are the least. No. Standard (British Edition) Monopoly game board layout. White Chapel and Old Kent road are the least.

It depends on where in the game you are... There are some great statistical tables at : http://www.tkcs-collins.com/truman/monopoly/monopoly.shtml One of the tables there includes "Expected Number of Opponent Rolls to Recoup Incremental Cost (assuming a Short Jail Stay)" - this is a statistical analysis of how many turns it will take to pay for the property itself plus any improvements. This might be a way to determine "least cost effective" properties. From this list, without any improvements, the top 5 least cost effective are (in the standard American version) the purple and light blue properties. Meditteranean Avenue ranks as worst with 1407 rolls needed to break even on the cost! Now, if you look at the list of properties with the cost of adding hotels, the list changes somewhat. The top 5 in that column are : Park Place (dark blue) : 45.73 rolls North Carolina (dark green) : 43.53 rolls Pacific Avenue (dark green) : 42.68 rolls Pennsylvania Avenue (dark green) : 39.99 rolls States Avenue (light purple) : 33.72 rolls From this information, we see that the dark green take the longest to make up the money spent to fully upgrade them, so unless they can be upgraded early in the game, they probably are the least cost effective properties.