if I were you I would book aisle + window instead of middle + window...
- if you have middle + window, the aisle seats will most likely be filled in the end because other people of course prefer aisle instead of middle...aisle seats will get filled first before middle
- even if someone really got assigned to the middle seat, I'm sure he/she will very happily swap with you for either the window or aisle seat...I don't think anyone would "prefer" a middle seat