I do like the stainless steel heavier rings better but for everyday wear the lighter aluminum ones stay on better. Sometimes I also use the nitrile o rings with it to keep it from falling off. My balls have a tendency to retract and hence why I like wearing tighter rings. My fav is the brushed gold aluminum ring - its light weight and goes well with my darker skin tone.
When at the gym swimming laps I like to wear the heavy stainless/chrome because the suit hugs it well. A second ring goes around my balls so it pronounces it even more. I wear a Kiniki tan thru with no lining ( I cut them out) and the chrome can be seen visibly glinting in the light.
Silicone, as mentioned by others, stays on better for all day use. I have thick ones and smaller ones. The silicone ones don't do well with oil and start to crack easily. I like to use alot of oil especially at the beach or just nude at home.
The collection keeps growing.