I have this idea about a twitter mashup and I've been doing some research over the last couple of days regarding which framework to build it with. SproutCore looks really nice (especially as it has a UI designer too), then someone suggested Capuccino (I am not to keen to go with Objective-J, don't know why though). What do you think, stackoverflow-ians? (Note that it's going to be my first mashup attempt)
Really, it's too early to decide. They are both built on a strong foundation and have some great tools, but neither is complete or at that well documented. I've been tooling around with both on some small personal projects for a few months and there are parts of both that are great and parts of both that aren't. Its really up to personal taste and which community you think you'll want to be most active in.
The good part though, is that it shouldn't take you too long to get up to speed in either of them. I suggest you run through the tutorials on each page and just pick one and go with it. If it ends up not working out after a day or two, just switch. Even if you dont already know objective-c cappuccino's learning curve isn't that steep.
tutorials:
sprout core: http://wiki.sproutcore.com/Todos%C2%A0Intro
cappuccino: http://cappuccino.org/learn/tutorials/