Hi, would like to share my experience of buying downlights, having change the lights for 4 to 5 times before all settle! Hence very important to go to a shop that allows you to exchange. Below is my trial/ error and findings .

We decided not to use LED downlight as recent research shows that that LED can lead to blindness, damage to retina. Hence go for CFL. To determine what to choose depends on your

Ceiling height ?: If height is about 9ft,  6 inches type with 18w x2 bulb, frosted glass can cover about 6ft area. If not bright, you can change the glass easily to half frosted type/no glass type. If want brighter go for day light color. Warm white is the dimmest color.

Ballast or non ballast type? Lamp with ballast can tahan lama, but also noisy and hard to change if it is spoilt as you need to take out the whole unit of casing from your plaster ceiling.  If you put in room,  go for ballast free type (ballast can be noisy in small area) . If put in open/big area, noise is not noticeable.

Space in the plaster ceiling?  If only 2-3 inches height, LED is the only choice. This is especially so for bathroom which may have limited space due to piping running on top of plaster ceiling. Can only get made in china product as Taiwan have not come out with slim type.

It is energy savings lightbulb (stick or spiral type). The max watt/ type will be  fixed, depending on the type of downlight casing that you choose.