You can find the answers in my book, The Piercing Bible:
Initial jewelry style: Ring-style, commonly a circular barbell, or a septum retainer
If you are able to openly wear facial jewelry, a captive or fixed bead ring is suitable. The size should be proportionate to your nose and not so large as to interfere with eating and drinking. A 1/2-inch diameter is a reasonable maximum for most people. A very large, heavy ring could be dangerous to your front teeth when you run or jump!
A septum retainer is effective for concealment because the U-shaped piece of metal flips up and hides inside your nostrils. Though acceptable, a retainer is not the best initial jewelry because it can get knocked out during cleaning, nose blowing, or sleeping. Also, it isn’t as attractive when you do want to show off your piercing. Short barbells or plugs with O-rings are sometimes used as retainers, but these are difficult to clean and don’t show even if you want them to, so they are not the best options.
The circular barbell is a functional and versatile style because it can hide like a sep- tum retainer if you are not free to reveal your piercing, but it is also attractive when you want to put your jewelry on display. A small diameter (usually 3/8 inch) circular barbell is superior for concealment, comfort, and safety. The gap between the two balls allows your ring to be flipped up, so that the jewelry hides in your nose, but a ring that is too large will distort you nostrils from the inside. On most builds, a circular barbell will be as hidden as a septum retainer; however, if your nostrils flare higher than your septum, some metal will show. If you require maximum concealment, charcoal-colored jewelry is best because it is darker and less reflective than shiny steel.
Your piercer can widen the gap on your circular barbell so you can wear the jewelry up with the balls still in place. It should have a snug fit when inside your nose so it won’t fall down at inopportune moments, though this makes it a little challenging to change its position.