Don't have a 137, but between my 81's and 012's, the shures sound flatter, even, nice tone, but not "3 D" or with much textural dimension. Very nice and well-built mics though.
The Oktava's sound less flat but more flattering, not as accurate but prettier sounding, with depth and character. Built to Russian standards. I have the 012's both modded and stock, the mod sounds smoother, quieter, fuller, the stock sounds peakier, more colorful, a touch of self noise on very quiet sources with high gain.
Sonically, I'd take a good modded 012 over the 81 any day. Stock, the 81 is a nicer mic, would be a closer call. IMHO. YMMV.
Ed Billeaud - Snowflake Studio
There is no justification for the exploitation of weaker beings. We cannot advance as a species until we respect the rights of other species. One Earth, all earthlings. http://www.soundclick.com/edbilleaud