Short answer, wait until November if you can. New iOS and Android coming out. As well as more Win8 regular tablets coming out.
It's really a tough call.... Surface 2 is nice, but without apps it just seems so expensive. On any given day I use about 5 apps on my tablet. MS Office... Meh, I have a work laptop for that and a 24" desktop...
The Surface 2 really goes after a niche... People on a tight budget, who need office, but don't need comprehensive multitasking, but also don't really need apps, yet want portability. It's essentially students. You can't really multitask too much on a 10inch screen....
The T100 is nice, but it only has 2GB of ram... I actually wouldn't recommend any Win8 (regular) with just 2GB of ram... Win8 (regular) uses more ram than Win8RT.... You have bay trail with 4GB, but Win8 doesn't support it yet...
In the end, i see the Surface 2 and love how it looks, how it feels, the specs, and love its potential, but at its price range.... Meh... 450 is nice, but without the keyboard it's not really a competitor against android or iOS.