The Godfather II

Every controllable business in the game comes under one of nine categories. If you own all businesses of one type then you own the crime ring.

Owning a crime ring comes with bonuses. The crime rings and bonuses are as follows:

Prostitution - The family gain knuckle dusters and inflict more hand-to-hand damage

Diamond Smuggling - Bulletproof vests that halve damage for both the family and your guards

Construction - Blown up businesses rebuild at double speed

Gambling - Double firearm damage with guns

Drugs - Drugs income doubles

Arms Smuggling - Carrying capacity for explosives doubled

Gun Running - Improved ammunition capacity

Chop Shops - Armoured cars become available at hideouts and Chop Shops

Adult Entertainment - Lower guard costs

You’ll own the prostitution crime ring early on in the game. Diamond smuggling is the next easiest as it is a small number of locations all in Florida.

After that I’d recommend drugs as it’s also easy to control and whichever other rings work best for you.