What he said above it seems to be a grab-bag.
For example, Fotodiox is usually my go-to brand when it comes to lens adapters, be it Pentax-K or Tamron Adaptall. I also have a LTM to Micro-4/3rd adapter from them but I found that it was pushing my lens just too much past infinity most notably with my Canon 35mm f/2.8 where I couldn't focus closer than 9 feet. They told me this was by design so that all kinds of lens could achieve infinity.
There was two possible fixes to this, one being to shim it, the other is to try a different adapter. The latter solution worked nearly perfectly for me by getting a Fotasy branded L39/LTM to Micro-4/3rd adapter.
So different brands can have different results, and in my case a cheaper one did what I wanted over a more expensive one. But I would look at Fotodiox for something that's M mount (well anything that's not screw mount) since they tend to be pretty accurate and if they're not, they'll make it work if you don't want to spend much more than 20-30.
Film (Working RF): Canon 7, Fed-2A, Argus C3, Mercury II
Digital: Olympus E-M5, E-P3