my babies always grow really really fast in the beginning so i never invested in anything but prefolds and covers in multiple sizes for the early days. we just used the prefolds w/out a cover at home, and then did them up with a snappi and a cover when out and about (i always liked the bummis whisper wrap - relatively inexpensive and never had leaks). once they slowed down a little bit i got some other things, but the first 4-6 months were more or less exclusively prefold. i did invest in some one-size pocket dipes with my youngest and used those sometimes for long car rides and such because she really hated being wet. then we switched to ec store trainers around 4 months - and even though she was like 90+ percentile for height and weight, those medium fit her till she was well over a year old. though interestinglly i bought her some larges around 9 months and those fit too, and would still fit now if she needed them (she's 26 months).
if you have a peanut i can see spending some money on some fitteds, but for my kiddos a kissaluvs or other newborn fitted that would've fit them at birth would've been outgrown in less than a month. heck, my ginormous son outgrew his infant bucket by length at 2.5 months old
he was 28 pounds at a year, and people were always asking me if he was 3! my girls weren't quite that bad, but grew really fast and had chunky thighs, so it just wasn't worth the expense until they slowed down a little.
if i ever have another one, i'm going to do a pf with a belt - my SIL did this with her son and it was awesome the way the front flipped down and then got tucked back in. perfect for ec. when she went out and about in the cold weather she'd put a pair of wool or fleece split-crotch pants on with the diaper over. it was awesome, so simple and efficient. and you can get dozens of prefolds for what a few AIO trainers would cost.
the other awesome thing about prefolds is that they are so versatile once you're done with them. i dyed a bunch of ours and now use them as un-paper towels in the kitchen, and DH took some of the more stained/beat up ones out to the barn for shop rags. in fact we still have some shop rag diapers from when my 7 year old was an infant. i also gave a bunch away to a friend who has a horse farm and she said they're the best farm rags ever
the environment is one of many, many reasons i chose to EC, so i like to do it as ecologically as possible. and prefolds are also the easiest to wash and dry - saving water on not having to do extra rinses and washes, plus super fast to dry and easy to line-dry.
