There are no opinions because they are virtually identical.
Not only in holdings but leverage, price to NAV premium, dividend frequency and with minor variations of NII and UNII. At one time I think there were slight differences in the percentage of tech stocks --- don't see this now but only glanced.
Their prices diverge from "logical" from time to time so a good entry spot candidate for intraday swings or wait 'til ex-dividend date if you're planning a longer term hold.
We own both, NCZ and NCV, having bought NCV in Sept 07 and added more for price averaging in Dec 09 and again in Jan 10. We acquired Ncz in Aug 10 and added more in Jan 11. We now have 6324 shares of NCV and 4260 shares of NCZ. Between the two funds, these are our largest holding. We intend to hold as long as we can and do enjoy the divvys. Would I recommend either? You better believe it. My opinion, for what it is worth. Good luck to you.