Freestanding vented dryers are generally the most simple and cost effective type of dryer. You can go for the more straight forward timed controller, which is a bit hit and miss, or go for the more accurate sensor drying system, which costs more initially but could save wasted energy.  Vented dryers must be vented out through a wall or window,  you will need the appropriate ducting kit and possibly installer to do this. Most vented dryers are supplied with a length of ducting.