There are a number of things to consider, including how important battery life is to you (the RT version should in theory have the edge in terms of battery life) and how complex the programs are that you need to run (Surface with Windows 8 Pro will have a big lead here). And remember, there are other brands bringing out Windows 8 tablets, including Dell
Surface with Windows RT ships with a version of Windows 8 called RT. If you're considering the Surface for work, think of Windows RT as being a tablet-specific version of Windows 8.
So what do you miss out on by going with Windows RT? The big one is the ability to run programs designed for Windows 7 or earlier versions of Windows. You can add programs, but only from the Windows Store - like the iPad and its App Store.
Windows RT also leaves out a few Windows 8 features like
Windows Media Player
Windows Media Center
HomeGroup creation (you can join an existing HomeGroup but you can't create a new one),
The ability to join a network domain.
This is by no means an exhaustive summary of the topic, but if you're considering getting your first Windows tablet then the above points are worth thinking about.