Light tanks are best for scouting overall because oil is more useful than metal or currency (unless you're at the stage where you want lots of emblem chances) but they die quick due to low durability.

High durability lets you scout longer, with heavies being best for if you're going to work or something. While the non-dps check damage is % based, once you go over 8 hours the dps checks start getting larger and larger so high durability is still useful if you need a tank to last 10+ hours (my own record is a 5* level 38 heavy that lasted 21 hours; that was more just to see how long it could go than to be useful)

Stats to put on scouting tanks, ranked from best to worst:

HP > Damage > Accuracy > Damage Reduction > Attack Speed > Evasion > Damage Bonus > Crit Chance > Crit Multiplier

0 effect: Penetration, Range, Movement, Rotation

Side Note: Are we SURE accuracy buffs scouting? I know its impact on dps is minimal, and is mainly used for countering evade tanks