Out of the several I've used and the many I've seen on customer cars in the past I am still very much an advocate of Synapse. On a MAF car they don't make much sense with out the anti-stall kit. Having the valve open at non boost times is ideal when there is a long distance from filter to throttle body (ie: FMIC). This would act as a turbo bypass for a more responsive driving experience while not in boost.
As far as the size of the opening (flow) honestly that size is more than enough. As an example, take a look at Borg Warner's EFI turbochargers with a built in re-circ BOV. This is where the industry seems to think bigger is better and its just not the case.
While I've no personal experience with Forge's diverter valves, I've heard some good things about them.
Noise and such is more for the user, but as far as your turbo/engine is concerned, the speed of operation and ability to not leak is what matters at the end of the day. On a side note, on MAF equipped cars, it is less than ideal to vent any metered air to the atmosphere. Technically it should be recirculated back to the turbo inlet pipe. :wink:
Edit: Also I would have to agree that Synapse has a tainted reputation as they have gotten into at least one major online 'bash fest' with Tial. As far as I'm concerned both Tial and Synapse have made fools of themselves yet both offer great products. That being said,I still prefer Synapse and I've been using their BOV's for years without trouble.