Hi, here's some role suggestions from my experience.
My favourite roles could be likely arranged in this way:
Camper = Tac leader > Sprayer > Sniper > First fragger >> Aimstar > Hacker > Newbie > Pistoleer > Whinner
I don't recommend to assign roles after ">>" sign because they are less likely to earn much in most occasion and i will explain it below.

Some roles are recommended to assign in this way:
A great aimer: Sprayer, First fragger
A great Sniper: Sniper, First fragger, camper
Player in great team: Tac leader, camper
Newbie: newbie, Pistoleer


Camper: player survives a round +140; player dies -65.

Uses: i assign this role when i'm quite sure the team will beat the opponent
easily with big score margin, thus less chance of death of the player.
Example:if a player dies 5 times in the whole game and his team win the game, he will earn you: (16 * 140) - (5 * 65) = 1915.(1000 max. earn)

Tac Leader: win round +75 ; lose round -75.
Just similar case to role "camper", if the player's team wins, you surely earn money. this role is easily to assign - if you think the player's team will win but some of your favourite roles are already assigned, just give him "Tac Leader". This role earn you the most when the player's team win with 16-0. :)


Sprayer: Colt / AK frag: +85 ; Fragged by Colt / AK: -85
the variable "the numbers of death" this time do not affect role "sprayer", so you can simply give this role to the player who have great aiming skill.

Sniper: AWP Frag: +100 ; Fragged by AWP: -200
A great sniper should wear this role. Be cautious that the money deducted if killed by awp is two times more than killing someone with awp.

First Fragger: First frag: +200; First death: -200
this role is the most interesting role as it's hard to know who will get the first frag/death. this role sometimes could boost your team's value if wisely assigned.(A sniper assigned with First fragger will be a nice option as awp always do a first kill)

----------------roles below are not recommended--------------

Aimstar(?): money earned if your player wins 1onX ; lose fixed money if K/D <=1
Actually i don't know how this role works as i always got "$0" earned when a player using this role. I guess 1onX situation only works when all of the player's teammates are dead and he's the only one survived.
I will leave a question mark for this role here and you can discuss with it. :)

Hacker: fixed earning with rating >= 1.2
i don't like some roles with fixed earning such as Hacker and Newbie. The money earned/lost from these roles are limited. If a player with over 1.2 rating he probably can earn much more if he wear role like Sprayer. If you have limited choices of role you probably will assign the hacker role. :]

Before sharing my opinion about the roles Newbie, Pistoleer and Whiner, i want to write a background information first: (:D)
As we know, the player value could be affected by the following variables:
____________________
Kill +550
Survived round +300
Two kill round +200
Three kill round +450
Four kill round +800
Five kill round +1250

Round started -500
Suicide -200
Team kill -500
____________________
From the above table we could know that, a player make few kills and die in every rounds will result in heavy loss in player value(could be 5~10k loss in only a single match). The value earned by roles probably won't recover it. That's why i won't use roles below in most occasion.

Newbie: fixed earning with Kills/deaths ratio <= 1
If the K/D ratio of the player<=1, it is no doubt that player value would decrease(rarely increase if that player makes some 1v5s :D?). Assign this role only if you're forced to buy the cheapest player(probably losing money) when you don't have enough money. :)

Whiner: First death: +200 ; Survived round: -140
Player value will increase when the player survives a round(+300), you will lose $140 if the player survives. And the main point is that you never know who would be the "First Death".

Pistoleer: Pistol frag: +300 ; Fragged by pistol: -300
When will we use Pistol in a round? The answer will be first round of 1st half/2nd half and the round that we don't have enough money to buy rifles.
If we buy a player, we always assure that his team will win to earn us more money, thus in this case the opponent will have a greater chance to arm pistol as they are losing rounds. You have higher risk that your player will be fragged by pistol.

That's all of my personal opinions about player roles, feel free to discuss and share your thoughts. :)