The .COM has the traffic and the mindshare that the new gTLDs do not have. If you are launching a site that you want to be popular at a global level rather than a country level, then .COM is the obvious choice. The brand name is left of the dot. That's where the real work is done in getting people to accept a site. This goes more for review style sites as it would need something special to differentiate it from all the other review sites. If the .COM is occupied with the choice of words, then try to work out a different combination and register it in .COM and where necessary .REVIEW and .REVIEWS. The thing that most people miss about TLDs is that it is a continually changing market. Even in .COM, approximately 2 million domain names drop each month. Approximately 43% of the domain names registered in .COM today will not renew next year. If you are targeting a country level market, use the ccTLD. In a country level market with a strong ccTLD, the ccTLD is more important than .COM because in a lot of countries, the .COM is not the most important TLD i that market and most of the new registrations each month will be in the ccTLD.
The choice of words for the domain is important. You have to think of it as creating a brand rather than just a combination of words. People refer to Google rather than Google.com and to Facebook rather than Facebook.com. The key to developing a strong brand is that the brand matters to people and people remember it. The TLD part becomes psychologically invisible to people. If you are targeting the US market, the .COM is the de facto local ccTLD and people will automatically assume that a brand has a .COM extension. This is an important thing to remember if you are going to develop in .REVIEW or .REVIEWS. If your domain name is example.REVIEWS, then people might automatically append a .COM to the end so that you will lose traffic to exampleREVIEWS.com. or even exampleDotREVIEWS.com. This is the power of .COM and how people think of it. It is going to take a lot of marketing so that people see some of these new gTLDs as real extensions. The good news is that REVIEWS is operated by Donuts and it is quite good at marketing. REVIEW is operated by Famous Four Media. If you had to concentrate on a new gTLD for this experiment, go with the Donuts operated REVIEWS but also register the .REVIEW variation to protect your brand.
The position of .COM is not likely to change in the medium term and it is still going to be the top global TLD in terms of recognition and registrations for a few years yet. For the moment, concentrate on the .COM as the primary brand but also register the equivalent .REVIEW and .REVIEWS domain names. It will be some time before the new gTLDs gain market recognition so the .COM will be a good domain name until that happens.
Regards...jmcc