I think my favourite age is from about 2.5 to 3.5 as they are old enough to do a lot of different activities, to learn a lot of things, etc. I like 12 month olds as well as they are little and sweet. The age I dislike the most is actually from about 17 months to 2 years as I find that is when they suddenly start getting into stuff, testing limits,running away from me outside, etc. And they are too young to understand the rules yet...takes a lot of training at this age and then by 2 or 2.5 they are much easier as they know the basic rules and limits.