Both of the lenses that you mentioned have great versatility in the range of zoom that they offer, as well as have a great price. They are not super heavy, so they will be great for traveling. I would go with the Sigma since you get a larger range. However, if night photography is important to you, I would suggest looking for a lens with a lower f-stop. The lenses you are mentioning have f/3.5-6.3, a better option would be a Sigma / Tamron 28-70mm f/2.8 if the night shots are important to you. The lenses above are fine for casual photography, the 28-70 has less range, but landscape design in Maryland is of higher quality in that range.