True, some anime is dubbed very well. Princess Mononoke comes to mind. As far as Cardcaptor Sakura goes...I find Sakura's voice kind of annoying either way but since I never watched it this way before, I wanted to check out the sub. I remember the heavily edited 4Kids version from back in the day so...yeah. As long as the voices are good I do like dubs, don't get me wrong. I'm no 'purist' either way by any stretch.
crunchyroll's library is pretty good, imo. They have a good mix of new stuff and older stuff and they do simulcast some shows, though you need a premium account for that, otherwise the episodes are available after a week. I'm there mostly for Fairy Tail, honestly. But I've seen some good stuff available. Rurouni Kenshin, Cardcaptor Sakura and newer shows like Sword Art Online, Sailor Moon Crystal. Also a number of long running shows like Naruto, One Piece, etc. Some, like CCS, are available in both subbed and dubbed versions.
The quality is decent enough, only 420p but hey, free and legal and most importantly for me, convenient. I'm only a casual fan at best so things like that don't bother me overmuch. You could probably find the same (or...better!?) quality on YouTube if you felt like digging through all the removed copyright claims. Or, you know, torrents. I also prefer to support the creators though, so I try to avoid doing it that way.