Interesting discussion...both cameras represent the low end of two cheap and mass produced companies. To be honet I wouldn't buy any.
HOWEVER...I discovered the Praktica B series, due to its cheapness and glass quality it has become my most used system, while a Praktica BX20 is nowhere built at the same quality standard than a Pentax LX, Canon F1 or Nikon F2 it is definitely comparable to a Pentax ME Super for instance, and I prefer the Praktica to those middleweight Japanese SLRs. Interesting enough the BX20 has a very good TTL Flash system and AE lock that the LX doesn't have, it's small and light, therefore ideal for street photography. Probably my favourite of the lot is the Jenaflex/BC3, but anyone when in working conditions works well.
For the L series, I have a VLC3 which was the latest attempt to make a professional camera, I would say it's pretty good, and a MTL50 with a dark viewfinder that to be honest was already obsolete in the 80s,
For Zenit, the 12XP is a good camera, if you want something comparable to a Pentax Spotmatic I think the 19 is a serious contender, so I would recommend that model especially if it comes with a Zenitar 50 mm f1.7.
As a general rule I consider DDR glass in good shape slightly superior to the Japanese top end like Nikkor, Canon and Takumar, in particular the Pancolar 50mm f1.4 is a killer lens, like the Flektogon and the zoom Vario-Sonnar, the Soviet also made a lot of good crystal but they never bothered to improve the electronics and the bodies.
unfortunately;not my expwerience;a brand-new Praktika bought in 1972 came with a shutter that lasted just one week before it broke.luvkely. I got my hard-owned money back and saved up for a Nikon FM,which I still have and which still works flawlessly. Noe they can be had for less than $50. It's an easy choice really.
You bought a FM in 1972?