I am Norwegian, so maybe a little biased ;) but I think that Drops yarn is really good quality. Unless you re prepared to spend silly amounts of money, I think this is the best brand to buy.
I have knitted clothes for myself which have been washed in the washing machine many times and they are still good ( this is even yarn that is supposed to be hand wash only). And I have knitted baby clothes for friends which as far as I know has kept well.
I can recommend the Alpaca (used this loads, it's very soft, this is the one I have washed in the machine on wool cycle)
Alpaca boucle is great for making garter stich looks great.
baby alpacca silk is lovely
Nepal is great for a more sturdy quality ( Lima and andes is same yarn only different thickness)
for cotton, I have used Safran, which is also very good.
Oh, and there is a sale at the moment garnstudio.com/lang/en/post.php?id=193
(saralyn reminds herself that she is on a yarn shopping ban until she has finished up everything that is filling the cupboards)
I have also used a few of the other Drops yarns, so feel free to ask me before you buy.