I think it ussually defaults to zones for me, but if you have the magnet enabled in the selection tool you should be able to shuffle through the different options by pressing TAB.
You should get feedback from ArchiCAD about which element you will select. Both from a highlight and at your mouse cursor.
Zone stamps ussually have a few hotspots (black circles) that show when you select the zone. These are also easy spots for selecthing zones and not accidentally geting a slab as you described.
I find that pressing SHIFT when trying to select things pops up a nice blue outline to quickly give visual feedback about what you will be selecting.
Finally: activating a tool and then trying to select things will give priority to elements drawn with that tool.
Erwin Edel, Project Lead, Leloup Architectenwww.leloup.nl
ArchiCAD 9-24 NED FULL
Windows 10 Pro
Adobe Design Premium CS5