As stated above, "comfy" and "best view" aren't readily available together for the average guest viewing Fantasmic! Personally, we think the best view is from the Dining Package viewing areas (so BB, RBT, or HB) right up by the water. If you can sit on the ground reasonably comfortably (and the BB package does come with a firm foam cushion), you will have a good/great view of the show. All the dining package areas have good views, so choose which menu and price point work best for you. If you want to sit on a chair and eat dinner during the first show, you can book the RBT Premium Dining Package (book by phone only) and view from the RBT patio. This is "comfy," but not, at least in my opinion, a great view of the show. The RBT patio is further back and off to the right somewhat. If you are not seated up front at the railing, you will be seated behind other parties who might obstruct your view. If you book a VIP tour (expensive option just for F! viewing), you will be allowed to sit (on a chair) in the reserved seating section for VIP guests behind the Dining Package (on the ground) viewing areas.
You can do a search on this forum for threads on the F! Dining Package options to read reviews of the menus and to see photos and some videos taken from the various viewing areas.