Ratskin Scout
Easily my favorite hire gun, they tend not to impact too heavily in game but that's not what you hire them for. Guide and Explore are abilities that make the ratskin scout worthwhile.
Guide guide gives you a +/-1 on the scenario roll regardless of who is underdog.
The amount of times the +/-1 to the scenario roll has given me the choice of scenario alone makes a Ratskin a near permanent presence in my gangs over the years.
Explore allows you to use the ratskin to look for a new territory for you if you win a game. On a roll of a 6 you find one, on a 1 however he leaves your gang.
In game I tend to use them sparingly, preferring to allow my gang members a chance to gain wounding hits before I let the Ratskin shoot. (Often just to ensure an important enemy gang member is pinned)
They often have a mobility skill with skills such as Leap, Sprint, Dive and Infiltration. This makes them ideal flankers, send one off on one side of the board and your opponent will have to divert at least one member of their gang to deal with the Ratskin. Even if the two never actually end up attacking each other that is one less ganger for you to worry about.
Underhive Scum
These gunslingers add some fighting punch to any gang. With an impressive 6 upgrades they are the equal of a ganger with 101 exp! With no long term injuries! And although some of the upgrades they can roll are not the best they are still all at least relevant to their role. Their initiative is doubled in shootout, but as you don't choose who participates in shootout it is down to chance if he will even be there...
I personally don't use them as I would rather my gang gain exp than pay a guy to take it for me.
But still they are a cheap and effective hire for a underdog gang.
Bounty Hunter
Very expensive. Very well armed. Very deadly. (At least at the start of a campaign)
These guys are great but by hell do you pay for it! Used correctly though you can use them to earn extra credits, but at the cost of your friends.
They have a special rule that means if they down a fighter in combat they are automatically captured. A good use of this is to down fighters using shooting then charge in with the bounty hunter the next turn. This would make him very unpopular with other gangs so he would quickly become a huge target.
Repeat rescue missions or paying ransoms will soon get old for the other players.
Buying Screamers, Bioscanners and Infra red goggles makes it even harder for successful rescues to take place,.
Bounty hunters quickly become outclassed by members of gangs though once a campaign gets going. Hire wisely.