I'll share my experience with you.
I have a 8GB SDHC Card(Un-Branded) - Class 4
Never had any problems with this card, Reads perfectly fine, saves fine albeit a little slow but nothing to worry about.
I have a 4GB SDHC Card(Also Un-branded) - Class 6
It was better at Read Speed and Write Speed on my pc so that'll cut time putting games on.
It reads perfectly fine in the DS and it saves much faster than a Class 4 Card.
I have no experience with Class 2 Cards but their are slower at reading and writing, so on pc it'll be slower for backing up and writing games, they may have lag in game-play as some say and they probably save pretty slow too.
I would recommend future proofing, spend a little more and get a Class 6 card.
They go pretty cheap(About £14 for an 8GB Class 6 Card) and are worth it for the extra speed.
I dunno much about Labels and such as I've not had any experience with them, both my cards came un-labaled, but they did have Taiwan on them, so either there's a company called Taiwan or they came from there lol
Hope the info helps