If you're going to hunt with it get 7.62 X 39. If not, get 5.45. Well, there is one thing to consider: in all the likelihood 7.62 X 39 barrel will outlast 5.45 X 39.
You should treat the claims along the lines of "Russian troops want 7.62 X 39 back" the same as "US troops want .308 back" i.e. as mostly BS. I get a chuckle out of “troops prefer this, troops prefer that”. Russian troops prefer what is issued to them by the Ministry of Defense. And the Ministry of Defense is very much happy with 5.45, is phasing out AKMs as fast as the money allows and is not looking back.
The development of 7.62 X 39 “urban” round has nothing to do with a rekindled popularity. Fact of the matter is this particular 7.62 X 39 is just a part of a recently developed “low ricochet” ammo line that includes ALL small-arms calibers currently in employ by the Russian Military/ LE, from Makarov to Mosin. Exception being 9 X 39 which is considered inherently low ricocheting. This ammo line, coded PRS, was designed by Barnaul primarily with AKS-74U and 9mm Para sub-guns in mind and Ministry of Interior, not the army, being the customer. To my knowledge 7.62 X 39 PRS had never even been officially accepted, let alone issued. 5.45 PRS is at least authorized by the Ministry of Interior for some people like Court bailiffs.