Starcraft – Does the Infestor’s slime trail ever serve a useful purpose

You can use the bug report forums: US forum, EU forum.

Short answer: There is no difference except for range and animation.

Long answer: They both do the same damage, have the same cooldown, and benefit from the Zerg range upgrades in the same way.

Roach Claw Attack

• Damage: 16
• Target: Ground
• Cooldown: 2
• Range: .1 (melee)
• Upgrade: Zerg Missile, +2 per level

Roach Spit Attack

• Damage: 16
• Target: Ground
• Cooldown: 2
• Range: 4
• Upgrade: Zerg Missile, +2 per level

(source)

As for which is better to employ, the spit attack is better simply because it keeps your roaches at range and allows more of them to hit a target while leaving melee range for units that only have a melee option. Your roaches will naturally use their spit attack anyway, so there's really no difference in your micro. They just fall back on the melee attack when they are next to whatever they are attacking.