Considering the amount of videos Youtube hosts no wonder some take longer to load than others, and some are of low quality. Some times YT messes around with the quality (on AC AMVs anyway), but the long loading times are primarily due to the file size which people load, so it theoretically isn't youtube's fault...
Where i would I be without Youtube eh...well i'd use other hosting sites but as far as convenience goes Youtube is easily the best, its simple and easy to use for everyone and members can subscribe to peoples vids, create favourites list and join several Youtube groups where people discuss anything from Naruto to Indian Food...in short Youtube is great.