Dead Age

The best place to find Suits is on Highway Day/Night. The Highway, both Day and Night versions, are available right at the start of the game. Because Suits are one of the earliest enemies encountered in the game, this may be the second or third "Kill 10" achievement you will unlock (after Bitten Pedestians).

Only zombies labeled as "Suit" or "Underhanded Suit" count for this achievement.

Suit Stats
Fast: Yes
Immune to K.O./Stun: No
High Defense (aka needs Breakthrough): No
Special Abilities: Bite (Bleeding DoT), Low Blow (Stun)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 5
Locations: Highway Day/Night

Underhanded Suit Stats
Fast: Yes
Immune to K.O./Stun: No
High Defense (aka needs Breakthrough): No
Special Abilities: Shriek (Summons Bitten Pedestrian when hit)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 2
Locations: Highway Day Night (starting at Area 11), Woods Day/Night