To answer your question I took nutritional values of some of the popular vegan alternatives. I compared:
- Sweetened and unsweetened soy milk
- Sweetened and unsweetened almond milk
- Rice milk
- Coconut milk (Alpro, not the "real thing")
- Oat milk
Nutritionally closest possible match would be sweetened soy milk.
As you can see, it has really similar nutritional values for fat and proteins. The carbohydrates are about half of the cow's milk even though it is sweetened. You can add some sugar to it if you want. It contains marginal amounts of salt, but rather close to the cow's milk. Due to the fortification, it contains the same amounts of vitamins and minerals as regular milk. It also has some fibre, which, although not what you drink milk for, is not bad to have in your diet.
All of the other milks I compared were not as close to cow's milk, mainly regarding the fat and protein content.
Values are per 100ml until stated otherwise.
Cow's milk (Whole/3.5%fat):
Energy 268kJ (64kcal)
Vitamin B12 0.4µg (16% of NRV)
Calcium 120.0mg (15% of NRV)
Soy Milk (Alpro, Sweetened):
Energy 161kJ (39kcal)
of which saturates 0.3g
of which sugars 2.5g
Vitamin B12 0.38µg 15%*
Calcium 120mg 15%*
Since you are looking for good milk substitute I would suggest you to look at three things when choosing your vegan milk.
- Protein content of around 3g
- Carbohydrate content not lower than 2g
- Fortification with vitamins and minerals like B12, Calcium, D or even B2
EDIT: Based on your comment, I edited my answer to include information you asked about.