Vent Hood for GE Profile

We're building and I am trying to decide on a vent hood for our GE Profile. Probably will stay with the GE because that's what our builder offers. There is a GEJV566HSS for $409 and a GE Profile 36" Designer Hood for $765 through the builder. The Designer hood does look nicer, but they are comparable in performance. Could someone please tell me what's the most important thing in selecting a hood...I know to get the cooking odors out, but what else??? Also what is the "Sones Rating"? The one for $409 shows Sones Rating: Rear Exhaust of 7.5 and Sones Rating: Top Exhaust -Round 7.0
The Designer Hood shows: Sones Rating: Top Exhaust 7.0, Vertical Exhaust-Round (Cubic Fee/Minute 600); it does not show a rear exhaust in the designer specs. If anyone has one of these, please let me know how noisey they are. Help! I need to make a decision. Is a vent hood something that is easily replaced after I build.