If your shooting needs call for both a tripod and a monopod, you might want to consider a convertible tripod. While generally more expensive than a straightforward tripod, convertible tripods are essentially a tripod and monopod in one. Just unscrew one of the tripod legs and attach it to the head when you need to use a monopod.
Ideal for: Mixed uses (e.g. travel, studio photography, time lapses, landscapes/architecture, sports/action, wildlife, live performances)