Are all milks created equal?
You have probably noticed an explosion of choice in the milk section of your supermarket, particularly on the shelf. With increasing numbers of consumers choosing vegan lifestyles, and the perception that non-dairy milks are 'healthier' a whole new market has opened up for manufacturers.
Firstly lets just clarify, all milk is nutritious and beneficial to your body. Dairy milk is low GI, high in protein, calcium, magnesium, phosphate and Vitamin B12. Making it naturally the most nutritious (providing close to 10g protein and 300mg calcium per 250ml serve) of all the milks. There is a myth that 'skim milk contains higher amounts of sugar', or that 'when they take out fat they replace it with sugar'. This is completely incorrect. Skim milk does contain minute amounts of increased sugar (0.5g/250ml serve - so less than 1/10 teaspoon), due to the very small concentration that occurs when the fat is removed. This 0.5g is largely insignificant when looking at your entire daily nutritional intake. Given the fat in dairy milk is an animal based fat (and thus predominantly a saturated fat) it can increase cholesterol levels. So if cholesterol is a concern, best to not be a "milk-o-holic. But if you are only drinking milk in your tea it really won't make that much difference which milk you choose if you are not drinking large amounts.
Lactose free milk is a great first place to look if you are concerned milk isn't 'agreeing with your digestion'. It has exactly the same nutrition profile as regular dairy milk with the addition of lactase (the enzyme that breaks the lactose double sugar molecule into single sugar units). Otherwise it is exactly the same and mostly available in full fat, low fat and skim varieties.
Soy is the closest plant based milk that resembles dairy nutrition profile while being naturally lactose free and low Glycaemic Index. It's protein content is almost the same and most soy milks are fortified to 300mg/serve (with some as high as 400mg/serve), although contains no Vitamin B12 (as is all plant based foods do). Soy milks also contain good amounts of isoflavones (which are protective against heart disease and LDL-C (the 'lousy' one). Often people (women) are concerned soy products increase risk of breast cancer, however 2 - 3 serves/day have been shown to lower risk of all cancers (including breast cancer).
Almond or Macadamia Milk
Almond and macadamia milks (and other nut milks) are increasing in popularity with the perception they are 'more healthy'. While they are naturally lactose free and low in saturated fats, they also contain minimal protein (<10% that of dairy and soy milks), calcium and carbohydrates (so provide very little nutrition overall). Most are not currently fortified with extra calcium, although this is changing (so make sure your almond milk contains at least 300mg calcium/serve). It is certainly not suitable for anyone who struggles getting sufficient protein in their diet or are underweight.
Similar to almond milk, rice milk is naturally lactose free and contains very little saturated fat, protein or calcium (unless fortified). However these milks are very high in carbohydrates (mostly double that of dairy milk) so not a great choice for people with PCOS, diabetes (or pre-diabetes), liver disease or wanting to loose weight (plenty of hidden sugars)
Likely the least popular of all the milk alternatives, and very similar to rice milk above with some extra fibre (5g/serve). However, oats are a gluten containing grain and in turn this milk is unsafe for people with coeliac disease.