Both lenses you are looking at are nice and the best answer will probably depend on what you most want to do with your first additional lens because they are each meant for something different.
I've collected a few lenses (understatement

) since getting my a700 last May and have the 18-
250 and the 16-80. Since I bought the kit without a lens I first picked up the 18-200 but returned it when I found the 18-250 used at almost the same price in order to get the added zoom. It also has a metal mount and if I recall correctly the 18-200 has a plastic mount. Just something to be aware if you weren't already when considering the purchase. That makes it lighter but could potentially make it more prone to breaking in the event of an accident like dropping the camera. All that being said I haven't heard of any problems with the 18-200. Getting a lens with that range was definitely a good choice for me since those lenses are really quite good and very versatile.
Later I found a used 16-80 so I picked that up as well and it is now the lens that I use the most - probably b/c a large majority of my photography is landscape. The lens is sharp and there's a little something extra to the colors IMO.
I'm happy I'm able to have both lenses and I think I bought them in the correct order for me. Since you do have the kit I'm going to guess you'll like having the extra zoom more than the added quality. If I had to go down to only one lens I'd be very torn over the decision but as much as I love the Zeiss I would probably have to go with the 18-250 because of the versatility. If I could keep more than one the Zeiss would absolutely be one of the keepers.
Let me throw one other option out to you..35% off on the Zeiss is a very good deal - I don't think it will be too often you run across that if you really think it's a lens that would want. If you do go with it and later on want an ultra zoom the Tamron 18-250 is as highly rated as the Sony version and is less expensive, although not in the 35% off price you could have on the 18-200.
Hopefully something in my ramblings will help with your decision and that I didn't confuse it more by throwing in another lens!