We are in the middle of building an audience before our Kickstarter launch (hopefully in the next month or two) and we are using all three. Because this is my first crowdfunding project, I'm very new to these platforms. However, this is what I've experienced so far.
Prefundia - Easy to setup and use. Nice paid promo offers. They seem to have the largest network and do have the predictive analytics however, the spread is quite large. They do track your views and allow followers to sign up. Prefundia keeps postings up after they launch and has a separate section for launched projects making it easy to find you once launched.
Pitchfuse - Easy to setup and use. Allows users to tweet, facebook like, etc.. right from your posting, as well as, access to the posters twitter and facebook pages! They tweet your posting once activated! Very easy to navigate and is laid out well. Keeps postings up after they launch and has a separate section for launched projects making it easy to find you once launched. Still in beta but definitely worth using.
LaunchRock - Easy to setup and use. Landing page looks really nice once complete and is laid out beautifully! Lots of features and analytics. it's great that you actually get the sign-up email so you can directly communicate with them. I do wish they had a way of searching their Landing page database (maybe they do and I just haven't found it yet). For our project, this has offered us the most sign-ups.
We like and continue to use all 3! Obviously, Twitter and Facebook are also great tools to build an audience.
Links to my pages:
http://prefundia.com/projects/view/swoo ... eans/1407/http://www.pitchfuse.com/project/swoosh ... cleans/342http://swooshlenscase.launchrock.com/