So, in terms of emulation, Android can do:
- everything 16-bit and 32-bit
- N64 to a certain extent and PSP almost flawlessly
- has slightly better battery life (depends on the tablet)
Desktop Windows(also known as x86/x64 Windows, like the one found in the Surface Pro 3) can do:
- everything 16-bit and 32-bit
- N64 decently well(Project64 was updated recently, if I recall correctly) and PSP flawlessly
- PS2 and Gamecube/Wii if the processor is strong enough (I believe the Surface Pro 3 should handle these at native res)
Portable Windows(like the one found in the regular Surface 3) can do:
- pretty much nothing
I'd say pick up a Surface Pro 3 if you don't care for the battery that much (especially of you're going to emulate, which drains the battery for 2-3 hours) or get something like a Nexus 7/9 if you want something cheaper with better battery that isn't as capable.
If you ask me, seeing as you'll use the tablet purely for media consumption, I'd recommend an Android device, since it just does a better job.
Windows tablets are meant for people who want to do work on the go (or play League/Dota 2

).