1) I don't have these lenses, but it is my understanding that both of them are quite good for "kit" lenses.
2) Both of these lenses are capable of producing "professional-looking" images. Are you?
3) If you are referring to a wide angle lens for "general landscape use", there aren't any AF-S primes that are very wide on a DX camera. The new 28mm f/1.8 is a "wide normal". The 24mm f/1.4 (expensive!) will only get you to the equivalent of 36mm on DX.
AF-S TCs aren't made (and won't fit) to use on most lenses; primarily for telephotos.
I would use the lenses you have unless you want a wider zoom. In that case get a 10-24mm, 12-24mm, or maybe a 16-85mm (and leave the 18-55mm at home).