My worst mistake was trialling nappies for 2 weeks and then going mad and buying loads of the ones I thought I liked best.
I imported Happy Heinys from America because I wanted them in colours that I couldn't find in this country. I have used them a bit, but they tend to leak after about 2 hours so I'm trying to sell them at the moment, though no-one is interested

. I also bought 6 Tots Bots easyfit as I loved the idea of bamboo AIOs but they have never worked on DD so they are also for sale now.
I wish I had known to look for pre-loved nappies when I first started - in the last couple of weeks I have bought some gorgeos WNSS and Itti Bittis - they are great and no more expensive than my other nappies that I bought new - and you can't tell the difference between the pre-loved stuff and the stuff I've had from new.
My best buy apart from that is my Nature Babies bamboo loveables - I use these at night and have never had a leak in them, even after 14 hours. I bought them direct from the manufacturer on ebay and they were only £5 each, but they work like a much more expensive nappy