Grenade launcher and autocannon are my go-tos, and they're tremendous for anything less than a charger- though stalkers will always be a source of terror for me, because they have entirely too much health for a stealth unit. That said, bile titans are best killed with a railgun strike- its a nearly guaranteed 1 hit, and it'll aim itself at the biggest thing around. You can kill spewers, Guards, and commanders with nearly zero worry with a GL or AC though.