The engine of Paksuzuki swift is without VVT, hence the higher consumption. Also, swift has 15" 185 width tyres, and 70 kg extra weight. V2 has 14" 175 width tyres. All of these things contribute to swift's higher consumption.
As for V2, it's engine is of course 1339 cc, but marked as 1298cc in papers. It has VCT technology (variant of VVT) and sequential fuel injection, which make it more fuel efficient.
Swift does feel cramped in the back seats, has lesser leg room and boot space as compared to V2. Swift has 210L boot space and V2 has 320L. But the interior design of swift is ages ahead of V2. V2 has airbags and crash beams in all doors. Don't know if swift has crash beams or not. As per my experience, Paksuzuki didn't provide crash beams in cultus as well, so they might not have provided them in swift either, but not sure.
V2's headlights are electronically adjustable, swift doesn't have this feature. Suspension of V2 is softer as compared to swift. V2 has better comfort, swift has lesser body roll on turns.