Errands- in and out of the car- having an impatient 17 month old waiting- I love my K'tan. Great for that purpose.
Don't like my Ergo so much for that, it's pretty bulky and with wobbly head- I had to buy a heart2heart insert, which makes it even bulkier. (DS2 is 11 weeks, o.k. head control, but no enough to go unsupported).
Didn't like the sling either for reasons of weight distribution, and bending down to pick up a pair of "lost" shoes from DS1 ,or anything for that matter, was an issue.
So I go for the K'tan.