Bicep curls go with the heaviest you can curl without swinging the weight. If you cant curl it slowly and under control its too heavy.
There is some use in a swinging on a bicep curl, but only once you've exhausted strict reps, or you're concentrating on the later half of the bicep curl movement.
As I mentioned in another thread. Make sure that by the end of your last rep of your last set for that particular exercise you are finding it nigh on impossible to do without screaming, shouting or crying and perhaps bleeding a little. So choose an appropriate weight that by the end you achieve the above. If you struggle to do your full amount of sets/reps the weight is too heavy. If it's too easy, the weight is too light.
Chin ups.