very wide topic ler..
u use for what?
movie? work?
use in home, office, bright light? dim lit?
where u put the projector?  short distance? hang on ceiling?

what resolution u want?  640? 1080? 4k?
other functions eg android, wifi etc.

and.... whats your budget?

I already mention that I never bought and hardly know nothing about them.

Home entertainment, 1080, room chair distance to wall 2m, room 3m wide, android with wifi, budget under 1k

ok that limits to what are the possibilities

1. budget will be the constrain
an acceptable projector example will be rm1.6k. i think this is the nearest to what you want.

https://shopee.com.my/-FREE-SHIPPING-Xiaomi...0336.5939081447
2. compromises
https://shopee.com.my/BenQ-MS550-SVGA-3600-...8654.1362647568
non 1080
3. short throw, lasers etc will be much much higher prices. so can ignore them.
4. those odd brand one can ignore for no or hard to get technical support/spareparts.

Ok these are the information I needed, why need spare part? They need to be maintain regularly?
-->old design like the benq one needs to change bulb and filter
-->new design LED are not as bright but no need change bulb

Also I already edited my previous post, and thank you for your feedback.

So what important factor needed to consider when buying?
1) Lumens    -->higher better, means you dont have to close curtain when watch movie, or set to total darkness in room.
2) Resolution  -->higher more expensive.  1080p is a good place to start. those benq one are usually xga
3) Spare part availability    -->led most likely no need spare part. but need technical support/warranty.
4) etc

Can you list out what spec you consider first before buying?

i would consider the practicality first. why would u want projector instead of normal tv screen?
for rm1k you can get a good 32" monitor or 50"ledtv
for rm1.5k you can get 50" 4k tv

if want to get 100inch projector, you will need to sactifice lots of things and not cheap either. mainly is the room thing. you will get tired of closing the window blind just to watch tv.
unless its a dedicated movie room lah.
cheapest short throw laser is rm5.7k
https://shopee.com.my/Xiaomi-Mijia-Ultra-Sh...4358.1649748292

oh i see...
dont bother those rm200 400 ones. too dim to be useful.
even tested an expensive acer LED unit. pitch dark only can see things.

you might as well diy get old phone, get a magifying glass and shoebox.
https://www.youtube.com/watch?v=YfvTjQ9MCwY
diy 4k
https://www.youtube.com/watch?v=p8YCVdTtmZw
diy cheapo