It all boils down to this: do you need to be able to install and run desktop software?
If the answer is no - then choose Surface RT - you'll get everything you need in the store or via the web, and the app store market is growing rapidly.
If the answer is yes, then challenge yourself to really prove to yourself that this is the case. Take a look at the apps you'd want to run, and see if the apps in the Windows Store are actually going to do what you need. Remember, a Surface Pro is an Intel tablet, and will be heavier, thicker, and have lower battery life. It will be more powerful of course - and is effectively able to be a desktop PC when you need it to be, but if you're looking for that 'pure tablet' experience, then don't allow desktop software to compromise that experience - and go with Surface RT. I did, and I'm glad I did (I still have a regular desktop PC for the 'power user' stuff).