while awaiting Eddyz...
I've never driven an Allion (or Premio) only their predecessors but
online:
A15 (G Front wheel drive) - 6.1 L/100km - about 16.393 km/l -> performance 109 bhp (141 Nm Torque)
A18 (G Front wheel drive) - 6.2 L/100km - about 16.129 km/l -> performance 132 bhp (169 Nm Torque)
From prior experience with figures from this website, these are likely for consumption on the highway. In heavier traffic the margin would probably be higher, and additional, personal driving patterns contribute much.
Incidentally, the A20 (Front wheel drive) has 6.1 L/100km -> produces 152 bhp power (196 Nm torque) and has CV Transmission...
Of the three engines, I'd opt for the 2000cc (A20) due to the power / economy mix -> though most people wouldn't coz of the D4 phobia.