TAAGMA (Lieutenant) Breaker Combi Rifle, Nanopulser / Pistol, CC Weapon. (0 | 16) TAAGMA (Lieutenant, Hacker [Zero Pain]) Breaker Combi Rifle, Nanopulser / Pistol, CC Weapon. (0.5 | 18) KRIIGEL (Lieutenant) Submachine Gun, Phero-Booster, Pheroware Tactics: Eraser, Pheroware Tactics: Mirrorball / Viral Pistol, CC Weapon. (0 | 25) KRIIGEL (Lieutenant) Breaker Combi Rifle, Smoke Grenade Launcher, Pheroware Tactics: Eraser, Pheroware Tactics: Mirrorball / Viral Pistol, CC Weapon. (0 | 20) RASAIL (Lieutenant) Combi Rifle, Shock Mines / Pistol, CC Weapon. (0 | 34) CHAKSA PERIFERICAL Heavy Flamethrower / Pistol, CC Weapon. (- | 4) RASAIL (Lieutenant) Viral Combi Rifle / Pistol, CC Weapon. (0 | 36) CHAKSA PERIFERICAL Heavy Flamethrower / Pistol, CC Weapon. (- | 4) RASAIL (Lieutenant) Spitfire / Pistol, CC Weapon. (1.5 | 39) CHAKSA PERIFERICAL Heavy Flamethrower / Pistol, CC Weapon. (- | 4) BRAWLER (Lieutenant) Rifle, Light Shotgun / Pistol, CC Weapon. (0 | 15) NEEMA (Lieutenant [+1 Order]) Breaker Combi Rifle, Panzerfaust, Nanopulser / Viral Pistol, Shock CC Weapon. (+1 | 39) NEEMA (Lieutenant [+1 Command Token]) Spitfire, Nanopulser / Viral Pistol, Shock CC Weapon. (1.5 | 42) If you need a good and reliable Lt. that can hide and add additional command bonuses it's Taagma. If you need attacking Lts then it's Rasail or Neema. Kriigel can use his Lt. order to throw Mirrorballs and help other units to advance. Other options don't seem to be all that appealing to me. Note that Spiral has no NCO so if you really want to use Lt. orders then Kriigel, Rasail, and Neema as solo Lt.s are the only options for you.
Notably, choosing the Kriigel with Smoke saves you 0.5 SWC compared to his non-LT version, and he can form a cheap defensive fireteam with 2 Reex for +1B on his smoke. Hence he's usually my pick unless I'm going for some sort of Rambo LT like Unicorn mentioned.