For the sake of simplicity, describe the player's nemesis' areas of competence (I hesitate to say 'villain' because the players are so rarely the good guys*) in terms of 'average', 'good', and 'holy freaking krunk'. His/Her stats are 7, 9, and 12 respectively.
No-one should have more than one stat at 12.
General rule:
inept grunts - straight 7's with skills at level 0 in whatever areas they're called on to act in. Keeps the maths easy... give them level 1 if you want them slightly less inept.
competent minions - as above, but the two key stats (whatever they are) are 9's. One skill at level 2 and other relevant skills at level 1. This gives you 'professional' level. Don't ask the players to take them on in a straight fight unless they have (a) better equipment, (b) surprise or (c) a numerical advantage or someone will probably get killed. Remember, two accurate gauss slugs will generally put someone in ICU.
scary/scary dude - 'key' stat at 12 (or more), other relevant ones at 9. One skill at 3, two at 2 and three at 1. Shedloads of money (MCr+) spent on relevant implants and gear. Use only once or twice in a campaign.
Note; the above is not restricted to combatants. An EDU-12, INT-9, SOC-9, Advocate/3, Persuade/2, Admin/2 lawyer with skill augmentation, MCr5 in hard cash and a secure laptop with a Database of Interesting Facts (TM) is at least as deadly to the players as a thug in battledress.
To translate; if you want a fairly 'easy' gunfight where the players might feel threatened but won't be killed, take an equivalent number of inept 777777 goons with Gun Combat/0 and sidearms (at whatever TL the players are equipped to). Either no armour or something 'discreet' - cloth, ballistic vest, etc. This is a decent model for anything from crewman to slum gangers.
'Proper Soldiers' should be something the players will be running from, sneaking past, bribing, or anything but shooting at. 999777, Gun Combat/2, Recon/1, Melee(Small Blade)/1, Gauss carbine/rifle with laser sight, dagger, comm, combat armour.
'supersoldiers' are the sort of thing that happens if the imperial marine corps gets called down on your head. At this point, your chances of survival are directly linked to them wanting you alive and/or the risk of collateral damage. 99C977, Heavy Weapons (Autocannon)/3, Recon/2, Stealth/2, A VFR Gauss Rifle with a Biomass Rangefinder and Specialised Intelligent Weapon upgrade, Ballistic Tracking Lenses, Advanced Subdermal Armour and Battle Dress with Vislight Chameleon, Assorted Combat Drugs will probably kill everyone in a normal party if they are stupid enough to try and take him on. If this was a film, he'd be the bad guy's chief henchman and probably played by someone like Dolph Lundgren. You can't fight, you can't hide, but you might, just might, be able to run.
* "You are fooling yourself, Captain. Nothing here is what it seems. You are not the plucky hero, the Alliance is not an evil empire, and this is not the grand arena."