Which lens is better: KONICA 135MM F/3.2 HEXANON AR or PENTAX 135MM F/2.5 SMC TAKUMAR M42.
Better, as in sharper for micro shots attached to the EOS-M with some extension tube and an adapter?
I can't answer that question directly (I have the Konica Hexanon 135 3.2 and 135 2.8s from Olympus and Vivitar ($28!), along with the Canon 135mm L) but allow me to suggest another for you to consider as well, the highly regarded Vivitar 135mm 2.8 close-focusing - it's bigger than the standard Vivitar 135mm 2.8 (though not as big as the Konica-Hexanon) but allows you to focus much closer than any of the others and, depending on what you want to do with it, this may make extension tubes etc. unnecessary (on the other hand, if mine's typical, it's probably not as good at capturing detail on distant subjects as the others I have). To find out more, this may be a good place to start (it's where I first learned about it, I think):http://www.pentaxforums.com/userreviews/vivitar-135mm-f-2-8-1-2-close-focusing.html
I should perhaps warn you, if you're interested, that this lens seldom shows up on ebay (I've never seen it at KEH/Adorama/B&H) and when it does, as often as not it's not this lens at all but the regular Vivitar 135mm 2.8 misidentified (whether the sellers are clueless or devious I can't say) - but it's easy enough to figure out. All you have to do is look at the photo the seller provides of the front of the lens - it will have "close focusing" (among other things) written on it. (Despite the evident scarcity of the real thing, it's still not expensive - I don't think I paid more than $120 for mine, which seems to be in good condition and even came with its original case.)
All that said, you might find the ergonomics of the bigger 135mm MF lenses a tad awkward (to say the least) on an EOS M - they're all metal and even the smaller ones are heavy for their size compared to most modern lenses (I use mine on mirrorless Sonys).