what brand you wear
A mixture! Currently wearing a Bambino Bianco Ultrastretch, and my wardrobe also contains ABU Preschool, ABU LittlePawz, Abena M3, BetterDry/Crinklz, and cloth diapers.
how much you go through in a month
105-115 diapers a month, usually.
the average end of the month cost to refill your stock on diapers?
A touch over $200, although it can go up to about $250 depending on what diapers I buy and how much I decide to overstock.
What size/brand do you wear and how much it can hold?
I'm medium in most diapers. I use a bunch of different diapers for different things, so they can hold different amounts. However, I'm a tall, broad guy who consumes a lot of fluids. I'm also incontinent. As a result, I tend toward fairly thick diapers in my wardrobe. The thinnest are probably Abena M3s, and those are borderline uncomfortably thin/unabsorbent for me.
Is it best to wear a certain brand in the day and a different one at night?
I find that it generally is. The rationale behind this is pretty solid - during the day you can usually get away to change (I go through 3 to 4 diapers in 16 waking hours), but during the night you're asleep for 8 hours and therefore can't change during that time. You could simply wear a normal "thin" diaper and leak, but if you don't want to do that, it's better to get an "overnight" diaper which is a little thicker than your normal diapers.
Personally, I consider my M3s and Preschools to be day diapers, my LittlePawz, Biancos and cloth diapers to be night diapers, and my BetterDry/Crinklz to be somewhere in the middle.
what type of pants are best at hiding the bulge when you are in public?
It's more about what pants to avoid. In general, don't wear thin fabrics and you should be okay.
A more important concern is where the seams fall. On a lot of normal clothes, there's a thick, solid seam straight through the crotch. Those pants are designed for underwear, not diapers, so where they sit normally will cut into your diaper and could impair the function. In the front they'll be constantly squeezing it in the middle and could give you upper leg leaks; in the back they'll be pressing your diaper up against your butt, which leads to problems of its own if you go #2.
My recommendation is to get jean-look casual pants, or investigate aged care vendors, many of whom sell pants that have deeper crotches precisely for "personal care needs". It'll be a little less stylish, but I assume since you're diapered, having everyone see every line of your body is not a concern.
One tip: if you mess in public, and I don't think you should unless you're IC, but some will - be aware that messy diapers create a large, visible lump in the back of your pants, to the extent that you would have to tie a sweater over your but to hide it.
