Oh what a decision.
Personal: Stg44 The birth of the modern assault weapon and I don't care what the Russians say, they copied it.
Artillery: PAK88. Came a little late but awesome tank killer. Low profile, high velocity and accurate.
Armour: StuG III. Tanks are great but tank killers are better.
Aircraft: JU87. Aaah, the tank buster. Another tank killer. Did I mention I love the hunt....Pzjgr strikes again!