Hi,
Am sure there are plenty of comments around about the supple differences between the two architectures, but the bottom line is, in the broadest sense they both do much the same thing.
Seems you have not established what you are looking for, perhaps you should tell us a little more about what your aspirations are ?
First, what if any, is the particular area of micro control are you interested in, such as motors /robotics/ sensors / etc etc.
What programming language are your thinking of using, or say have learnt a little of at college - so many to choose from these days.
What about hardware have any thoughts on how much you want to spend.
The UNO is probably one of the cheapest complete starter kits, but will need extras buying for it depending on what you want to develop.
Other more expensive development boards already have things like lcds and extra chips fitted.