Choppas have a special mechanic called rage. You gain 5 rage every second you are in combat up to a maximum of 100. There are three stages of rage called normal (0-24 rage), furious (25-74 rage), and berserk (75-100 rage). Let's pretend this mechanic is a street light: green (normal), yellow (furious), and red (berserk).
Green means go. If you are in the green, you should keep hitting people with your basic attacks until your rage builds up. Yellow means caution. Yellow is a good color because you gain a 25% bonus to your attack damage when yellow but suffer no penalties. Yellow also means you can use most of your exhaustive blows (EB). EBs are special attacks that drain your rage to 0 (green) and give you a 75% bonus instead of 25% for that particular attack (if you are yellow). That said, you'll soon be at red, which means stop. Actually, whether you stop or not depends on your play style. Some people run red lights, right? While in the red zone you gain a 50% bonus to your attack damage but you also receive a 50% penalty to your armor and resists. EBs used while red drain your rage to 0 but does not grant a special bonus to your EB attack damage like it does in the yellow. Certain EBs, however, require that you are berserk.
While playing a choppa can never be considered safe, the safest way to play one is to use your EBs while in the furious (yellow) state. More aggressive choppas (read: psychotic) will spend most of their time in the berserk (red) state. As you'll see below, each mastery path takes advantage of the rage mechanic in a slightly different way.
Path of Da' Savage (PoDS)
"A mastery path focused on longer-duration battles."
At first glance, this path doesn't seem very special but you should consider a few things before writing it off. First, there are only two PoDS EBs: Keep On Choppin', an attack that gives you back 100 action points and Try and Hurt Me, an attack that reduces your target's chance to crit by 100% for 10 seconds. You will likely spend a lot of time berserk in this path. Second, PoDS abilities don't restrict you to one weapon-type, so you can dual-wield or use a big two-hander. Thirdly, you can train an awesome channeled ability called Furious Choppin' that does big single-target damage and heals you for all damage dealt. Finally, training this path will also buff up your core attack, Can't Stop Da Chop, which is huge armor debuff attack. Overall, PoDS is a great 1v1, leveling, and main assist spec. It is also quite easy to master since you aren't always worried about your EBs and draining your rage.
Path of Da' Hitta (PoDH)
"A mastery path focused on dealing quick, exhaustive blows."
The path works as advertised since it affects almost every ability with a furious or berserk prerequisite. PoDH is also the two-handed (greater weapon) spec, as many of the abilities require you to have one equipped. This path grants two powerful EBs: Tired Already, an attack that increases your target's cooldowns by 5 seconds for 10 seconds and No More Helpin', an attack that reduces the amount your target is healed by 50%. PoDH also features Bleed 'Em Out which is a huge DoT that I recommend for any spec (you only need 6 points in this path to get it). PoDH can be a bit more challenging than PoDS because you're focused a lot more on your EBs. The reward is pumping out some hefty DPS if you can get your timing down. Your spec-line and core EBs generally have good utility as well.
Path of Da' Wrecka (PoDW)
"A mastery path focused on area of effect offensive abilities."
If your goal is to hit as many squishies as you possibly can at the same time, choose this dual-wielding path. PoDW assumes you'll be running into the thick of it and actually offers a couple unique defensive abilities worth mentioning. Chop Fasta is an insta-cast buff and any time you are hit within its duration, you will reward your group with a half second reduction to their cooldown timers. Bring it On is a 10-second channeled self buff. Each time you are hit, you will reflect heavy damage back to the attacker(s). Pairing this up with a pocket healer can be quite devastating (if you're getting pounded on). PoDW is also home to the famous Git to Da' Choppa ability, which is a very powerful channeled AoE attack that pulls a random nearby enemy toward you. AoE attacks are generally weaker than single target attacks, but you're in your element against multiple foes.