frontier justice - able to do a lot of damage at close range and when you hit enemies with the southern hospitality it will deal a huge amount of damage on the enemy. But the only problem is you need to be fast and perform hits from behind this would be a good strategy to kill spy's that are standing there sapping you're sentry. Hit them with the southern hospitality which will make them visible if they cloak then shoot them with the frontier justice.
short circuit - The short circuit uses Metal but it is good for long range shots, if you have a sniper with you then they can hit the enemy with a jarate and then you can wipe them out easily with the short circuit because of its rapid fire ability
southern hospitality - this is possibly the best wrench (in my opinion) for the engineer, it is extremely good for defense against the enemy. Once you hit a enemy they will start to bleed and it will lower their health, if you continue to hit them it should kill them easily.
and a weapon I would not recommend using is the wangler, you need to be very experienced with this and practically it is useless. The fact if you hate you're sentry just because its pointing at the opposition then this is for you, even in Mvm it is stuff. Don't use the wangler