I definitely like pockets the best overall, although I do get burnt out on stuffing them sometimes. I haven't used too many AIOs.
I would definitely take the prefolds your friends are offering. They are GREAT for the first couple months and baby won't be able to wear the OS pockets quite yet. Even though I started at 6 weeks will my son, he still couldn't fit into most of my pockets so I ended up using prefolds as well.
My stash is neverending; I still need to get everything out and sort through it all. I have built up a lot over the years and so will you probably! I think I have 2-3 newborn pocket dipes that I used for outings. I have a few fitteds; mostly used those for overnight. And then I have a TON of pockets - all different sizes and OS. And lots of covers. Of course since I don't know what I'm having, I have to leave the girly dipes out for now...
I am especially fond of the Kawaii heavywetters! They really hold an amazing amount.
For fasteners, I love velcro when they're little because it's so easy to get a good fit. But once mine were toddlers they'd take the diapers off unless they had snaps.
big boy 12.8.07 @ 39+2 7lbs 8oz, 20.5" BFed for 13 months
middle boy 8.12.09 @ 39+4 7lbs 9oz, 21" BFed for 13.5 months
little boy 4.26.11 @ 38+4 6lbs 14oz, 19.5" BFed until 26mo and again 30-37mo
baby boy 10.25.13 @ 41+0 8lbs 15oz, 21.5"
8.16.12 & 12.16.12
surprise pregnancy ended 1.9.15