If you'll always be paralleling them, it might be worth looking at the Honda EU7000iS inverter generator. It would be a little more fuel efficient than the pair of generators, and according to the specs should be microscopically quieter (though in practice not enough to really notice).
One obvious disadvantage is that it's a lot heavier and more cumbersome to muscle around if you cannot wheel it into position than each 300W generator. Another is that, like all the Honda inverter generators, it's not exactly inexpensive.