As of right now I can't think of any reason to look into a Windows RT tablet. There's just not enough applications when compared to Android and iOs tablets, I think Microsoft is even trying to get away from RT.
If you are thinking of going with a full fledged Windows tablet then there would be a few viable options available. The current model Baytrail Windows 8 tablets (Asus T100, Dell venue, others) are capable machines and are at a similar price point as iPads and high end Android tablets. They have pretty good performance and decent battery life, but don't expect them to be a desktop or even a laptop replacement, they are still tablets.
The i series tablets are generally would be out of the price range of Andriod tablets unless you go refurbished. Currently the first gen Surface Pro
is $399 (Microsoft store usually offers 10% off for students, I don't believe you had to verify this in any way) which if I was currently buying a tablet would probably be the route that I'd go.
It all depends on what you use your tablet for. Heres my mostly unbiased analysis of your options.
A full Windows tablet is going to be a much more powerful option being able to run your desktop programs. Windows 8 is a much better experience on a touchscreen device then on a desktop or non touchscreen laptop, they are continually making improvements based on user feedback. I run a program called Bluestacks which is an Android emulator. It runs decently, there is some lag and loading times are long (the performance isn't amazing on my sig rig either, I think the software engine is just not very optimized) but I can play popular games like Clash of Clans that aren't on the Windows market place. The Windows Apps run flawlessly, there's just a very small selection in comparison. I actually really like the home screen, the tiles show my Facebook, Emails, weather in real time which is great for a quick glance. I'm a little biased to this since I have a Windows phone and really like it.
The pros of an Android tablet would be the huge market place, usually better battery life, better screens vs windows tablets of the same price. You can get some pretty awesome specs for around $400 like 1600p screens, high end mobile processors, lots of ram and internal storage. Depending on which model you go with you would have a lot of choice for accessories, more so then most Windows tablets. I think by the numbers Android has the most applications of the top 3 mobile operating systems. You have the most options in this category by far depending on if you favor or a certain company. There are also a lot of cheaper options in this category, though you'd need to spend $300+ to get a decent upgrade from your current model.
You didn't list iPads as an option, some people hate Apple and others love it and I'm not really biased either way. The iPad's have a really nice build quality and their appstore is on par with Androids. For same $400 you'd spend on an Android tablet you'd get pretty comparable specs and screens from Apple. I personally feel that the iPad is the best price vs performance product that Apple offers. There are also tons of accessories for iPads, more so then probably any other tablet on the market. Battery life is great, better then Windows and similar to Andriod, better depending on the model.