If one wants full capture and containment, the dual-purpose of a cooking hood, then two key parameters have to be achieved. The hood has to overlap the cooktop sufficiently to capture the rising and expanding cooking plumes from the burners/hobs, and the air flow rate has to be high enough to assure that the captured plumes are pulled through the filter and not allowed to reflect back into the kitchen. This requires sufficient air velocity at the hood canopy entry aperture. Adequate depends on what is being cooked, the temperature it is at, and whether the plume is augmented by gas flame combustion products. I suggest 90 CFM/sq. ft. of entry aperture (achieving 90 ft/min). This value times the entry aperture in square feet yields the required full power volumetric air flow rate (CFM). To achieve this CFM in the presence of pressure losses in the hood baffles/filter, duct, hood to duct transition, duct to roof cap transition, and significantly the make-up air (MUA) differential pressure achieved, requires a blower with a zero static pressure rating higher than the required flow rate. A factor of 1.5 may be a good starting point for analysis. It is easy to get to a rated 700 - 1000 CFM blower depending on cooktop size, although without more information we cannot determine the OP's actual need. In my view, the hood should be blowerless, and the blower should be on the roof. Typical down roof blowers such as Broan, Wolf, and Abbaka sell are one useful style. They have automatic dampers that open when active. The alternative is an appropriately sized up-blast blower such as routinely seen on restaurant roofs (only smaller) that has its own advantages and disadvantages (mainly heightened visibility). If enough duct length exists and space around it is available, a silencer can keep the blower noise down to conversational level. The OP should review the myriad hood threads on this forum, along with MUA threads, to gain an appreciation of the factors involved in adequate kitchen ventilation. For background, there are commercial reports that may be found on the Internet, such as from the California Air Resources Board. For a good summary, the first dozen or so pages of the Greenheck guide may be read. http://www.greenheck.com/media/pdf/otherinfo/KVSApplDesign_catalog.pdf

I think it really depends. Nothing that moves that much air is going to be quiet. If you can have remote blowers and inline mufflers, then you can reduce some of the sound; and in that case, a VAH might very well the obviously inferior choice. But even then, you still have the noise at the baffles. So, don't expect the hood to be whisper quiet. We have a 20 odd year old VAH. As long as the vent pipe is adequately sized, it works great and noise level is IMHO in the expected range. We also have a new ModernAire hood with internal blowers. It has more power than our old VAH, but it can be really really loud. And part of that is simply the whistling sound that the air makes when it passes the baffles at full air velocity. If I turn down fan speed, it's about as loud as the old VAH. In other words, I don't really perceive a big difference between either designs. Pick what works best considering all your other design constraints. And absolutely make sure that your vent pipe is as large as you can make it.

All blowers behave in a similar manner to the illustration below. As back pressure (or for that matter front negative pressure) increases, the flow rate drops. The goal with a given hood configuration is to choose a blower that at the pressure loss of going from outside into the house, plus past the hood baffles, if any, plus the ducting, back to the outside, the point on the curve where that pressure loss intersects (horizontal line) provides the CFM that the capture and containment function of that particular hood needs. Typical actual fan curve With this in mind, it is possible to have a blower rated at 1200 CFM mounted in a hood system and have the actual flow rate be only 2/3rds of that, i.e., 800 CFM. Because (as noted above) VaH use a different grease particle collection system, they try to compete by using a value that makes up for the (not necessarily what they assume) pressure loss of the baffles and hood transitions of an conventional hood. What is missing from the VaH claims, but now somewhat available on their web site, is the flow rate vs. the additional pressure loss. What are these missing factors? In the VaH case, these are the pressure loss of the make-up air system and the pressure loss of whatever ducting VaH didn't count. Of particular note is that the VaH fan curves are flatter at the higher pressure-loss region, making them less suitable in cases where either the ducting is long, angled, or the MUA is restrictive. The CFM can be rapidly degraded in that region. But all this is secondary to determining the actual required flow rate from first principles. In the case of residential hoods with low volume below the baffles, the flow rate needed is that which assures containment by the baffles of the cooking plumes that have entered the hood. I suggest 90 CFM per square foot of entry aperture. Commercial hoods can stand less when some plume averaging is achieved in the hood reservoir below the baffles, depending on what is being cooked. So the suggested approach is to take the value 90, multiply by the hood entry aperture (which should overlap the cooking zones) to find required CFM. Then multiply by 1.5 to account for all the pressure losses that are not known. Then select a blower that has that rated CFM. Note that rated CFM is measured in free air and is called the zero static pressure flow rate. P.S. If VaH is your cup of tea, be sure that it is being operated under the conditions for which it is specified. That includes perfect (no pressure loss) MUA.

This is not too helpful to note, but earlier threads of a few years ago addressed a hood that one could set an initial flow rate (among a limited number of values) and it would be "burned in" to the electronics. I don't recall the manufacturer. Trying some search terms might yield the topic.