I run an open source BPM/Workflow Software company called ProcessMaker (www.processmaker.com). We use the AGPLv3 license.
We had 3 employees in the company in 2006 when we were selling a proprietary version of our software. We open sourced the code in 2008. Since then our software has been downloaded 750,000+ times, and we are just over 100 employees in the company. In short - for us it was a very good move.
However, that was 2008. The world was a totally different place. I would not make that same choice today if I were starting an enterprise software company.
A couple more thoughts:
1) I wouldn't worry about a competitor forking - that will not be your problem
2) If you choose AGPLv3, you will probably also use a Dual Licensing model if you ever want to be a software company and not a consulting company
3) You would probably need to be a consulting company for a few years before becoming a software company if you want to have a community
4) 99.999% probability you will not get any meaningful code contributions if you use the AGPLv3. And 100% probability that it won't happen for a few years.
5) Look hard at whether or not a cloud based model wouldn't give you the same benefits of a freemium model that you are looking for - there are lots of reasons for this that are well known in open source circles. Most of my colleagues that started companies around open source enterprise software are now selling cloud software.
6) If your market is North America or Europe and you are building enterprise software, go cloud and forget open source.
Don't waste time or money with lawyers discussing license options. This has much more to do with a business model choice. I'm happy to discuss more with you, if you would like.