Should I start a piece with a magic ring or a chain ring?

A magic ring is one loop of yarn wrapped around your fingers, with the stitches of round 1 worked into that loop instead of into chain stitches. The loop is a single strand, so pulling the short tail makes the whole thing slide shut. A 6-stitch round in DK weight closes to a hole under 2 mm across, which is why no gap shows in the middle of a finished ball.

The trade is that the ring is only as secure as the tail. If you work round 2 without first tightening round 1, the loop stays loose inside the fabric and the centre never closes properly no matter how hard you pull afterwards.

A chain start works round 1 into chain stitches: chain 2, then work 6 sc into the second chain from the hook, or chain 4, join with a slip stitch and work into the ring of chains. The chains hold the centre open. In worsted weight that leaves a hole of roughly 4-6 mm that does not change size when you pull anything.

That fixed hole is a feature in two cases: when you are making a flat motif where round 1 will be hidden by a centre detail, and when you are working a mesh or net where the centre should be open anyway. It is a defect in amigurumi, where a 5 mm hole in the base of a ball is exactly where stuffing will eventually work its way out.

Work round 1 loosely enough to see the loop, then pull the tail before you start round 2. Pull in two stages: first take up the slack, then pull hard while holding the last stitch of round 1 between finger and thumb so the tension lands on the ring and not on the stitch.

After round 2, pull once more. The tail should now be trapped under the round-2 stitches; weave it through three or four stitches on the wrong side and trim. If the ring still gapes, you worked round 1 too tightly to move — undo it and go up half a millimetre in hook size rather than fighting it.