It's best to carry a variety, so you can put the most suitable pegs for the ground in the most highly stressed pegging points.
I would usually carry 4 pins, one of which is a 5 mm Ti Nail, 4 Y pegs, and 4 Ti V-pegs (gives me a couple of spares). I also carry a rubber walking stick ferrule to protect my hand when pushing them in. Using your foot is the commonest cause of bent pegs.
If it's hard and rocky, the Ti Nail can be bashed in with a big rock with little risk of damage, and I can then pull it out carefully and use the hole for one of the Al pins.
Y pegs are for regular grass, and the V pegs are for soft or sandy ground.
Cord loops in the top are worth having.