The design shouldn't matter as long as it is truly a pyx that is intended to hold the Eucharist and not a rosary holder or some other recepticle. The pyx that I prefer to use is a wide one, just over 2 inches in diameter and it is real thin and only holds 5 hosts. I prefer a wide pyx so that I can easily reach the Eucharist without having to tilt the pyx in order to be able to remove a Host. A wide and deep pyx can be heavy and bulky but the thinner ones seem to work best. If someone has to bring many Hosts, for example in visiting many patients at a hospital, then small diameter deeper pyxes might be the way to go. Again, I don't like the tilt factor so I use wider pyxes out of personal preference.