There's something about isobutyrate esters that's just so perfect. Butyrates often smell harsh and vomity (especially if impure or expired) whereas propionates can be that little bit too volatile. Isobutyrates occupy an aromatic Lagrange point, as it were.
 
Cis-3-hexenyl Isobutyrate is a particularly useful example of this functional group, with its green-fruity versaitility. Personally, my favorite place to use it is in florals like gardenia, Lotus, Waterlily, Orchid etc
 
Unlike Cis-3-Hexenol, which can have a harsh edge at higher doses, the isobutyrate can be used at higher levels with elegant naturalcy.