[updated 01/2017] This is an elemental damage and physical damage weakness overview for Warframe U19. This overview is a starting point for new players that want to progress through the starchart. This overview does not consider finisher damage, status procs and crit multiplier that are needed for high level (sortie or endless) content.
Physical Damage types and fraction weakness
Slash damage is good against Infested because effective against flesh
Puncture damage is good against Grineer because effective against armor
Impact damage is good against Corpus because effective agains shields
Grineer elemental weakness and best setup
Always use high Puncture weapons.
Grineer heavy units: Corrosive (Toxin + Electricity)
Grineer light units: Cold
Infested weakness and best setup
Always use high Slash weapons.
Infested heavy units: Corrosive (Toxin + Electricity)
Infested light units: Heat
Corpus elemental weakness
Use high Impact weapons.
Corpus heavy units: Magnetic (Cold + Electricity)
Corpus light units: Toxin
Void elemental weakness
When using Corrosive Projection:
Void heavy units: Radiation (Electricity + Heat)
Void light units: Viral (Cold + Toxin)
When not using Corrosive Projection:
Void heavy units: Corrosive (Toxin + Electricity)
Void light units: Cold or Heat
More info about Damage 2.0: http://warframe.wikia.com/wiki/Damage_2.018 People think it's helpful 😀