My experience in reflow ovens...
I was assembling high mix low volume (higher volume was farmed out).  All designs were sound (ie DFx).  Delegation to upgrade from thru hole to surface mount landed the choice of a 10-12 zone with Nitro.  At a cost of over 60K (used) I opted for the Heller 4 zone (thinks its a 5).  All the oven folks have this "Engineering" oven.  Brand new out of the box was 25K, I spent the remainder on additional ergonomic equip, an RF superMole and controlled atmosphere items that had high dividends.  A large issue, not to be underestimated is floor space.  The 10+ zoners are huge!  I think if you ask the question of which oven is best then you probably need the smaller.

Good luck,

Boston Brad