Both...they're pretty cheap enough to have both. I'm broke, and I do. Most say the C4s are limited to overhead use, though do it pretty well, where as the MK012s are better on acoustic and other sources,
and still good on overheads, but a little more colored and harsh...well harsh-er, they're not terribly harsh mics, but definitely a ton of character and some good color. C4s are crisp and clean in a good way.
I have done nice acoustic tracks with C4s...one especially in XY on a 1978 Martin D-28, which worked well
because the C4s are clean and bright, and that guitar is a tank...so thick and super-dark. Good on other heavy acoustics too. I do think they're a great price/performance mic.
Having both, and realizing you're asking one or the other...Oktavas.
I'm sure you've done your research, but be sure that they're real Russian-made. Chinese copies are running loose out there. So go through
www.soundroom.com only.
Some cool things about the MK012s is that you can Dorsey mod them if you want... although I think(not positive)supposedly the new ones have taken Dorsey's mod into consideration, so they really don't need the mod.
Nonetheless they sound great as is, and you can down the road get a collection of all the caps(C4s
do come with both cardiod
and omni), and more importantly the LOMO heads. That's the stuff. Red just came out with a "lollipop" LOMO style cap for the MK012s. It's $199. Me want. Check it:
https://www.gearslutz.com/board/product-alerts-older-than-2-months/72950-red-mic-introduces-new-capsule-oktava.html
Yeah get the Oktavas...