Hey,
I've tried the exam once. Maybe I could help a little bit.
1/. Personally I like la cambre better. But I know a girl who fail the entrance exam of antwerp are try la cambre. I think it's as competitive as Antwerp and I love the teachers there. You can't really compare both school, I think it's really depends on yourself.
2/. I once heard they prefer younger, fresh mind or not too skilled students. Because they don't want your knowledge to limit yourself.
I think if you are good enough and you impress them, then it should be alright.