Short guide to listbuilding:
Most important thing: healthy order pool.
It is somewhere betwen 6-7 for small games (150-200) and 8+ for bigger games (250-300). Only regular orders on the table at the beginning count. Hidden deployment or AD troops don't generate orders while they are not on the table. Irregular (Morlocks, Chimera) keep orders to themselves so they kind of don't count too for the purpouse of healthy order pool.
Specialist are nice to have but non-essential, especialy if you do not have clear idea what you gonna use em for. Hacker is sometimes useful sometimes it isn't. Heavy machine gun will always be useful. First pay attention to units you plan to do your killing with (usually those with SWC invested in them) then how to support them if you have points/room left.
True price of doctors or engineers is not the 3-4 points more you pay for them but orders you use to (try to) heal someone. You could be using those orders killing enemy dudes. Docs and engineers can be awesome but it is important to know when its beneficial to use them and when it's better to shoot more.
It's good to have variety in your list. Since you can invest your orders in whichever troop you want, you can channel them in one that has most useful skills at the moment. So it's good idea to have big toolbox of different troops and abilities.
If you want to know more I found this article very informative in the beginning:
http://thefrontlinegamer.blogspot.com/2011/08/building-infinity-army-plus-how-not-to.html
Automatically Appended Next Post:
I quickly cooked up a sample list that I consider both versatile, powerful and containing some of the troops you like:
NOMADS
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GROUP 1 (Regs: 7/Irrs: 2):
INTRUDER (Lieutenant) Combi Rifle + Light Flamethrower, Grenades / Pistol, CCW (36)
INTRUDER HMG, Grenades / Pistol, CCW (44 | 1.5)
ZERO (Minelayer) Combi Rifle, Antipersonnel Mines / Pistol, Knife (19 | 0.5)
CHIMERA Combi Rifle, Nanopulser, Zero-V Smoke Grenades / Viral CCW (21)

3x PUPNIK DA CCW (3)
MORLOCK Chain Rifle, Smoke Grenades / Assault Pistol, AP CCW (10)
SIN-EATER HMG / Pistol, CCW (34 | 2)
2x MODERATOR Combi Rifle / Pistol, Electric Pulse (9)
DAKTARI Combi Rifle / Pistol, Knife (14)
199 Points | SWC: 4
ARMY CODE:
Army Infinity v.3.0.
Intruder Lt - very hard to kill no SWC Lieutenant.
Intruder HMG - one man solution to most of your problems, especially if your problems hide behind camouflage or optical disruptors. Only disadvantage - slow.
Chimera - a beast in CC and fast.
Morlock - support offense. His smoke grenades have a combo effect with Intruders (intruders can see trough smoke with their msv2, unless it's zero-V smoke like the one chimera uses)
Zero - mines for defense, advanced deployment (infiltration) for offense.
Sin-Eater HMG - probably the most powerful defensive unit in game. Put in a position with commanding view. Disadvantages: Slow and useless in active turn.
Moderators - they provide orders. Codename "cheerleader".
Daktari - you can try how you like healing with this cheap gal. You can downgrade morlock to cheapest version in order to give her a helper bot (zondbot).
Both sin eater and intruders are worthy recipients of healing. Chimera can't be healed as she is a cyborg or something. If your uncouncious victims are under enemy view you can throw a smoke grenade to cover healing action.
I don't say it's the best list (hopefully a thing like this does not exist in Infinity), but it should give you an idea what I consider a good one.