@ Jarvy ... Interesting comment from you on pricing with BA/VS. Booking from this side of the pond [LHR-IAD] they always come up with the same cost [+- about £5].
However ... down the back, I agree VS and BA are fairly similar, I recall.
Up front it's a question of style/comfort/service.
T5 is not great, but better than T3. At least my overnight stop is in a hotel attached to T5. Cheaper hotels exist outside the perimeter, but then the cab fare to the Terminal quickly eliminates the difference!