John – this question keeps popping up and is a testament of the range of aspirations, skill sets and experiences out there in the industry.
I have seen them all and to date, I have not seen THE tool for landscape architects. We have to use various platforms to deliver the wide range of services we provide.
There are quite a few parameters to this decision, e.g. type of commissions, volume of communication with other consultants, licensing and price.
If you were just moving from a drawing board to CAD, I’d recommend Landmark. Its fans claim that it has maintained its “what you see on screen is what comes out of the printer” ethos. However, if you used LandCADD for years and generally happy with it then go for AutoCAD. AutoCAD on its own is very generic and is best coupled with add-ons such as Land F/X, GlobalCAD, KeySCAPE or LandCADD.