AVI, MKV, RMVB which format is better? which is the best quality?

Certainly MKV.
(CHILI) SAUCE: Wikipedia

If you are asking for quality, non of them, cause they are just multimedia container,

Currently the best video codec is H264, and the opensource implementation, x264.
and its competition codec, VP8, Ogg Theora, Dirac, FFmpeg Snow, and loads more which many info you can find on wikipedia yourself.

MKV > AVI > RMVB

there goes the answer..

MKV.. super clear

what do you mean by multimedia container?

MKV is not a video format, but a multimedia container format,
read here: http://en.wikipedia.org/wiki/Mkv
Yes MKV is the best... the best container.
The best video format currently is H264 and very soon, h265.

MKV video container with AVC/H264/MPEG-4 =

they are all multimedia container
rmvb most low quality，and i press one episode drama to rmvb ，need 3 hour
MKV is the best !

doesn't matter really, as long you have the correct software and codecs, you set to go.

btw those are media containerz, it is useless comparing containers.

i'm wondering on tis question too, looks like evy1 saying mkv is better.

why MKV is better?
it support all the audio/video codecs and subtitles formats, that rmvb/avi supports.

AVI is ancient container which cant support audio with VBR without hack, normally you will get audio/video out-of-sycn if mux VBR mp3/aac/vorbis/...(endless of list) eith conventional method.

Also, it cant support H.264 specialized B-FRAMES, Dxva/hardware acceleration does not work if your H264 in inside AVI.

while RMVB is exclusive for Real network's audio/video formant only.
they are outdated and no longer updated IIRC. so quality is far behind h264 already.

1 word sums it up for MKV = superior/versatile

mkv.
even the small sized mkv is far better than rmvb

LOL, dont know how to reply to this post
read the previous post by other member please, im pretty sure you know how to read

Hummm semua format tak best... saya pernah convert ke macam2 format kualiti selalunya ikut sumber utama. kalau sumber utama bagus maka baguslah hasilnye kalau sumber utama Cam awak convert ke blueray pun tak lawa tQ

x264 is the trend now.

Rmvb format is so terrible it changes my believe to not use it--

rmvb is not for high definition usage. its purpose of a much compressed size makes it friendly to users who don't have high bandwidth or capped bandwidth. it's also deemed suitable for those who still use crt monitors or tube tv's. not everyone has unlimited bandwidth, high bandwidth or lcd tv's u know.

The development of RMVB codecs a.k.a. RV40 stopped long time ago, basically the quality is much inferior compare to its competitor aka h264.

now their development only focus on the multiplatform video player.
http://en.wikipedia.org/wiki/Helix_(multimedia_project)