The type of formula you choose for your baby is really dependent on your budget, personal preference and lifestyle. Both liquid and powder baby formulas have their advantages and disadvantages. Also, your child may have a preference for one over the other.
Powder formula is cheaper than liquid or ready-made formula. The powder also last longer, so you are buying formula less often.
Ready-made liquid formula is the easiest to serve. It is already mixed and ready but requires refrigerating after opening. It is great for when you are on the go, especially when clean water may not be available. It is also more sanitary than using powder, because you just twist the cap off and pour it in a bottle. Powder formula is also pretty convenient, although it can be messy to mix. Also, if it is not mixed right, it can be clumpy. Liquid concentrate is the most inconvenient because it is difficult to travel with and requires more preparation.
Ready-made requires no preparation. You just pour it and go.
Powder formula requires a little more preparation because you have to measure out the right amount, mix it with water, and make sure it is mixed well.
Liquid concentrate requires mixing one part liquid to one part water but does not clump if not mixed properly. The downside is it does require refrigeration once it has been opened and is usually only good for 24 to 48 hours.
Powder formula is the easiest to find and is usually always in stock. Ready-made may be more difficult to find or may be sold out of stock more often.
Powder formula is the least expensive, so it tends to be the one people most frequently buy. However, those with active and busy lifestyles tend to go with ready-made formulas.