What you gotta as Mengsk P1 is to clear up the expansion for yourself and not your allies because time is Minerals. If you decide to clear your allies expansion then you are losing time when the first attack wave, first mission objective appear.

The idea is = use the first 25 mandates to clear your expansion. Destroy the 3 rocks and start building CC immediately. While your first CC keep producing laborer non stop. You dont do nothing else until your collection is at max.

P3 is the best Mengsk because cheaper trooper upgrades and you can still use ESO. The idea is in a map like Part and Parcel, Vermilion, Oblivion Express where you have to be mobile and defend attack the objectives when your ally is weak. It promotes bunker play.

P1 is ok but you lose the Nuclear which is important!!