Infiltrator / Commando is the sniper class combo, which is the more combat oriented of the two specializations. You simply target and kill enemies at max range with your trusty Sniper Rifle while they attempt to move into firing range. In areas where you can’t fight at long range, you have a good Pistol for backup. The Pistol also helps against Krogan and Husks that like to charge your position. This build includes high enough Electronics and Decryption talents that you can unlock everything in the game, leaving your squad to choose other skills (unless you also want them to have Sabotage and Overload skills).
12 Pistols (Unlocks Sniper Rifles, Marksman skill)
12 Sniper Rifles (Unlocks Assassination skill)
12 Tactical Armor (Unlocks Shield Boost skill)
6 Fitness (Unlocks Immunity skill)
9 Electronics (Unlocks Overload skill)
9 Decryption (Unlocks Sabotage skill)
8 Warp (Bonus Talent)
12 Infiltrator / Commando
12 Spectre Training (Unlocks Unity skill)
12 Charm / Intimidate
This build is all about your Pistols and Sniper Rifles with the other talents for support. You primarily use Sniper Rifles, but might occasionally switch to Pistols in short range. Tactical Armor and Fitness both also help in short range by giving you increased survivability. Fitness is kept low to leave more points for Warp.
Electronics and Decryption are both at the minimum 9 points to be able to unlock everything. Like Fitness, they are not maxed to leave room for a higher Warp talent. Warp is the only Bonus Talent I can see that works well with this build by reducing enemy defenses especially enemies that like to use Immunity such as Krogan.
Spectre Training is a very good talent for this class. It provides bonuses to both combat and tech attacks in addition to improved accuracy with weapons. The Infiltrator uses all of these, so it’s a small bonus to everything you do.
The Commando talents give you reduced Marksman, Assassination, and Immunity cooldowns, so they are your core skills. Immunity is really only needed when charged by melee enemies. Marksman and Assassination should be used as much as possible depending on the weapon you have equipped. Shield Boost is another defensive ability that tends to be pretty good with your enhanced shields from Electronics.
Overload is best against geth to remove a good chunk of their shields. Sabotage is good against almost all enemies, although they will switch weapons if their current weapon overheats. Warp is best against Krogan, Husks, and Varren to reduce their innate damage protections.
Damping instead of Warp – If you don’t care about Warp much, you can put those 8 points into Damping instead. Alternatively, you could put 6 of those points in Damping and 1 point each in Electronics and Decryption to improve them a little. You won’t be as good against melee enemies, but you will be better against enemy techs and biotics.
More Fitness instead of Warp – Immunity (Fitness) gets a nice cooldown reduction from the Commando specialization. However, we don’t really take advantage of that with only 6 points in Fitness. You could choose to skip Warp (offensive ability) in exchange for a maxed Immunity (defensive ability). The other 2 talent points can go into Electronics and Decryption or really any other talent of your choosing.