I chose to pay more for the LoveSac instead of getting a ComfySac because their inner liner was a heavy canvas, rather than a thin vinyl on the ComfySac, and they give you about double the foam inside the sac, which helps keep a more vertical shape when sitting. The less foam, the more flat, and/or close to the ground you will end up sitting (or in their case, laying). I preferred sitting up to laying down.
I also liked LoveSac's choice of fabrics. I was able to get a very rugged, yet SUPER comfy corduroy cover, rather than the thinner microsuede... LoveSac also offered smooth leather, suede leather, fur, and several other fabrics, that ComfySac didn't.
What I DO like about ComfySac, though, is that you can buy additional foam after the fact, and their warranty was a bit better. Ultimately though, I could buy the additional foam from ComfySac, and put it in my LoveSac if I ever felt I didn't have enough.
As for elmalloc's comment: go ahead and buy other furniture. These make very unique furniture that aren't for everyone. They are more difficult to get in and out of than your typical couch/chair, but they are MUCH more comfy and offer more flexibility in how you want to sit/lay in them... if you want chairs, get chairs. If you want a Sac type furniture, get these. Currently in my theatre I have one 6' LoveSac and a love-seat in the front, and a 4-person couch in the back row, to accommodate different preferences... Personally, I sit in the LoveSac for a couple hours of every day, and I only use the loveseat or couch on rare occasions.