I owned both of them and since my opinion is not as biased as some other people when it comes to CA I will tell you my way of seeing things.
Both of them has their pros and cons obviously. What I preferred about the Star is the way it operates and the auto winding boxmag feature is a neat thing. Sure the Star is plasticy but not everyone necessarily have the need to have a full metal gun.
Right now I got the CA and I only got it because I can't stand a plastic gun but that's my personal opinion. I find it annoying to have to push the little button at the bottom of the boxmag for it to wind but the fact that it can take regular AR mags is really nice. Another nice thing is how easy it is to change the spring in it, it's the only thing I did on mine when I had it and I never ran into gearbox problem just some boxmag connection problems which can be easily solved by changing the whole wiring.
All in all if you want to go for a cheaper alternative and that will be less of a workout to drag around all day go for the Star you won't be deceived. CA is nice if you have more money to spend on your M249 but be careful of problems you might run into with it. Another alternative would be to wait for the next Star MG, the MK46 which is basically a M249 Para with a RIS and railed feed cover.
Here is link to the MK46 :
http://www.starairsoft.com/product_d...?productid=205