It all depends on the volume you need. I own both the Gossamer Gear Gorillafor 3-season backpacking 1-3 nighters(BPL review here) and the voluminous SMD Starlite for winter camping and longer 3-season trips.(old version BPL review here).
I really like them both and they suit my purposes well. I took the Starlite on my Tahoe Rim Trail Hike and carried 27lbs in it for a 2 day dry stretch (9lbs of water to start, 4 days of food) and it carried fine, but I don't have back problems either. The Gorilla will also carry 25 lbs comfortably. Both loads were heavy, but my shoulders don't burn.. They tranfer weight well-enough for me, if not as well as an attached-frame pack.
The HMG Windrider is reviewed this week by BPL, and while I have not used it, it looks similiar to my Gorilla, if a bit lower volume.
Two other packs I tried before settling on the Gorilla were the ULA Ohm and the Osprey Exos 46 (BPL review here. I decided against the Ohm because I didn't like the hip-belt, an issue which I believe ULA has addressed, and I wanted a more modular pack that I could strip down when I wanted to.
The Exos also has a built in frame and I liked it a lot, I mainly decided against it because it was just more volume than I needed and it was 36oz (though if memory serves, the removable top lid weighs 4oz and is really unecessary) vs 24 for the Gorilla. But it carried very well and as the BPL frameless pack article points out, removable frame packs just aren't going to load transer as well as internal frame packs because the removable frames are not anchored to the hip belts. They work fine for me, but as I said, I've never had back problems. I'm generally fine up to 20lbs with a rolled up CCF as a frame.