@Max well , obviously... which is why the OP asked which player is good for .MTS files which is the extension of the AVCHD codec. WMP is generally crap and I always use VLC, but VLC is crap with avchd files in particular, whereas WMP isn't
VLC can play any file format because I guess has nearly every codec inside but quality seems to me quite crappy. Maybe WMP works well if external codecs are already installed on the machine. I'm looking at the KMplayer docs and it has all the codecs onboard. I'll give it a try
kmplayer has been superseded by potplayer, it's the same code base but cleaned up and actively developed.
the most accurate would be media player classic - home cinema (or potplayer) with madvr renderer. amongst other things, madvr supports the use of 3dlut files for colour calibration, but even without this has the best internal rendering (full 16-bit processing using video card pixel shaders) of any renderer. this setup requires a decent spec computer though.
the fastest (while still being accurate) would be media player classic - home cinema with its own built in dxva accelerated decoder (if your video card supports it) using one of the enhanced video renderers (evr, evr custom, evr sync).
both can be a bit fiddly to set up (madvr more so) unless you are willing to read up. unfortunately, vlc while being easy to use out of the box, is a jack of all trades and master of none.
it looks like there is a relatively new high quality decoder LAV CUVID http://forum.doom9.org/showthread.php?t=160290 which is worth investigating (allows dxva decoding and hardware deinterlacing while using madvr renderer). You would use this instead of your player's internal decoder, or external decoder if you are using ffdshow, coreavc, etc.
I use XBMC for playback. It works so well for reviewing footage that it has become a necessary element in my workflow. Performance is really strong for MTS files and high bitrate footage so far.
GOM player is my favorite, though had to install CoreAVC for it to work properly with GH2 files, always worked great with GH1 files. Has frame by frame advance, will automatically load all files in folder so will just play continuously (can disable in preferences) can set priority for which codecs to use for which types of video extensions, can zoom in while playing and move the image around (real time pan and scan) can do batch screen captures, can select which video rendering method to use if any at all, plus many more options