Symfony & Zend probably have a bigger ecosystem of consultants/support people if that's what you need? Symfony's documentation can be a little... 'interesting' sometimes though. It's many years since I looked at Zend's. Scalability usually isn't much to do with the framework itself.
But if you're writing it yourselves from scratch it's maybe more of a 'pick one and see how you get on'. IMHO you'll get a working product a lot quicker with Laravel.