I though I'd post a pic comparing sizes of my PUL covers:ImageUploadedByTapatalk1346131417.556522.jpg
Sorry I can't rotate the pic easily on my phone.
On the left is:Thirsties X-small, Bummis super brite Small, Motherease Rikki small.
On the right is: Bummis super brite newborn, Motherease Rikki newborn.

Bummis and Thirsties seem almost identical in cut to me but are different in terms of sizing. The Rikki leg gussets don't seem as good as the others but I like the fact they're higher rise at the back.

My squish is still under 3.5kg despite being 5 weeks old. Both the newborn sized covers fit her well and the X-small Thirsties are ok but slightly loose. The others would swim on her.