I only discovered anime in January, so I'd better not try and nominate a BEST EVER, but would like to list in order of loveliness those of which I've watched more than a couple of episodes so far:
- Ichigo Mashimaro, all 12 eps x 6 times
- Card Captor Sakura, both series and both movies
- Kodomo no Jikan, OVA + 7 eps (+ 32 manga) so far
- Pita Ten, all 26 eps (+ 50% manga)
- Lucky Star, 8 eps so far
- Pani Poni Dash, 6 eps so far
- Hidemari Sketch, all 12 eps x 2 times
- Moetan, 5 eps, including 2 without subs so I had to read the 'body language'
- Chobits, all however many eps
- Tokyo Mew Mew, all 52 eps
- PGSM, 24 eps so far
- Sailor Moon, 22 eps so far
- Kanon 2006, 13 eps so far
I think I would probably like Kanon more if I managed to focus more on the plot and less on the loli when watching anime, but I always think Ichigo will be top of my list