I can't really help you pick the best MVC framework, but I can recommend that if you are moving your Flex 3 projects to Flex 4, make as few changes as possible for moving components right now. Like you said, we are in the middle of a transition. The Adobe guys recommend not porting all of your mx Projects over to Spark. I have a large Flex 3 project that I'm almost finished moving to 4.1 and I have changed as little as possible. The only reason I converted it was to take advantage of some of the nice things they've done with data services and binding.
I don't think it is a waste of time to take Flex 3 projects and make them run in Flex 4.1 or higher, but I do think it is a waste of time to convert all of those components over to their Spark counterparts at this time.
Thanks for your reply Curtis,
I have already done exactly what you mentioned, and transitioned my projects to run using 4.1 with minimal problems. Aside from some of the new namespace requirements and package declaration changes (FlexGlobals, etc.) , I've tried to keep everything else that didn't require change the way it was. I just really hope that there is some consideration given for those who have invested a lot of time and effort to transition from Flash Pro to Flex (Flash Builder) in the future.
I'm just not a big fan of Flash Catalyst right now (at least not the current release). But if you want to skin your components using vectors, it seems to be a requirement and not an option. But it's basically just getting in my way and causing me to do something else in order to achieve the same results that I used to in the past. It's another moving part of the process that is only necessary because of this new 'efficient' and 'flexible' component architecture (which, in my opinion, is neither).
Thanks again for your response, I appreciate it.
Maybe you want to go to the Flex 360 conference next month. I bet they will be close to the next version of Catalyst which will be 2-way with Flash Builder and there will probably be a lot of resources to tap into on the best way to skin with vectors.