Like you realized, there is no best anime, like there is no best house. Different series have different goals, and should be evaluated based on these.
Claymore is a good example, it's a excellent an excellent remix of traditional fantasy elements. Not original, but very effective.
Rozen Maiden is also quite good at what it aims: loli/harem/gothic fetishism with a twist.
Full Metal Alchemist is a great "young boys go adventure" type of series. It delivers action, fun, and even manages to feed in a lot of plot twists and raise interesting issues.
Mushishi is very good at delivering beautiful and moody philosophical short stories.
Chobits is the ultimate "beautiful robot girl for desperate loners". The main robot girl is appropriately attractive/loli/bland, and the cute little robot girls are really cute.