Wider suspension is better, but changing wheels doesn't change the suspension. The best offset is the stock offset because it's the offset for which the suspension was designed to work. Reducing offset to "widen" the stance of the car does not generally improve handling. The suspension geometry is adversely effected. To correctly widen the track of the car, the suspension would need to be modified. And not just by changing parts, the entire geometry would need to be redone.
2015 STi: Still Stock
04 STi, 04 WRX: SOLD