This season: Log Horizon OR Kyoukai no Kanata. Log Horizon probably goes a bit higher in the tier for me.
All time: Clannad OR Spice & Wolf. Clannad for the many feelings it brought to me (Also the only anime to have made me cry tears, most others just make me watery); Spice & Wolf for it's light, elegant and fun storyline and how it actually develops the protagonist's relationship at a healthy level and shows them actually caring for each other.