all great ideas but i don't think a big knitting project would ultimately fit into the popincourt (as cute as it may be). and most knitters usually have a couple projects or more going on (if they have knitters ADD like me haha) so i'd go for the sac plat or the neverfull or for sure. or perhaps the bucket! there's also the notions and other things to carry too!
get one of the popincourt bags and u will be one true knitter in the LV sense (i think popincourt was first created to carry knitting needles and yarn )