Bought 2 king size both medium although according to their sizing chart, my husband and I would both need the firm. We LOVE them! We are both in our late 40's and I had started having a lot of back and neck pain after waking up. My husband has had several neck surgeries so we were both on the perfect pillow for us hunt.
After I started using MyPillow, all of that went away. Bought it in a TSV last fall and I have taken it with me where ever we go. I forgot it last month when I went out of town and had to use a hard, firm pillow that was in the room. Woke up with with a crick (spelling?) in my neck. I can promise you I won't forget it again! Lesson learned. I do plan on buying 2 more king size sooner or later but in firm only because I want another one for the base of my back when I'm sitting up in my bed watching TV. I love that you can push the insides of the pillow around and it will stay the way you need it. We had spent a lot of money on pillows over the past several years trying to find some we like. Never found THE ONE until this pillow and was actually surprised that we would both end up liking the same pillow brand.
Everyone is different and the only way for you to really know is to buy it and try it. You could have 50 people tell you that they love their MyPillow and 50 that say they hate it, but it comes down to what you prefer. And the only way to know if you like it or not is to use one. Good luck finding your pillow! MyPillow may or may not be what you are looking for. It was for us.