Both skills give equal bonus:
Trigger Happy - lvl1 5% ; lvl2 10% damage with automatic
Make 'Em Count - lvl1 5% ; lvl2 10% single shot damage
Weapons affected:
Trigger Happy - HP5, Kpist, AI-76, AG5, AG4, KVM 89, KVM 59.
Make 'Em Count - HP5, AI-76, AG5, AG4 (in semi-auto fire mode)
Unconfirmed for Make 'Em Count - Möller, Klaucke, Sjöqvist shotgun, 12G shotgun, .243, .270, .50 cal
As far as skills go, that depends on play style. But sniper is all about accurate shots over long distance. So, for sniper, Trigger Happy skill is useless. And to get that skill, you’ll be spending 5 skill points, that could be used for other skills, either to unlock new ones or improving existing ones.
For sniper build, the following skills help the most: Marksman, Make 'Em Count, Component Damage (3rd skill in left Tech tree).
Marksman removes ADS sway, making your shots very accurate. Make 'Em Count gives additional damage in semi-auto fire (e.g AG4 + 4-8x scope in semi-auto fire, which i love to use) and Component Damage increases damage you do against machine components.
Armor Damage and Trigger Happy, while useful, are mainly meant for those who doesn’t go after machine components and are firing at the general direction of the machine. Sniper, in the other hand, should focus on components, hence the Component Damage skill.