In my opnion, we should follow the official name where possible, and practical.
- [wii] (official name)
- [snes] (as [super-nintendo-entertainment-system] is way too long.)
- [xbox-360] (and not [x360] or [microsoft-xbox-360])
- [playstation-3] (and not [sony-playstation-3])
The only system i have some trouble with is in the Nintendo DS family (more precisely, the Nintendo DSi XL) however, in my opinion, using the official names is still practical here.
- [nintendo-ds] (most common and most general)
- [nintendo-ds-lite] (usually only for hardware questions etc.)
- [nintendo-dsi] (for DSi specific questions)
- [nintendo-dsi-xl] (least common, very specific, also, [dsi-xl] is a bit unreadable)
- [nintendo-3ds] (what does [3ds] mean? multiple 3D?)
Also, in my opinion we should use [gameboy-advance] instead of [gba] to match the [gameboy] which isn't [gb]
Taking Tobias' idea from his synonym request, is it possible to have alias tags? This is one feature I'm not clear on with StackExchange.
If it's possible to have alias tags, I think it would be beneficial to have [nintendo-wii] alias to [wii],  alias to [xbox-360], and so on. That way, no matter which way someone types it, they will correctly classify their questions.