I can understand your desire for an opening hole instead of a thumb stud or similar protruding device; it allows full use of all the blade's surface and also permits ambidextrous handling when necessary.
If you're looking for alternatives to Spyderco, I can suggest the CRKT Nirk Tighe models. The full line of Nirk Tighe and Nirk Tighe 2 offers models in 5-1/4", 4-1/4", 4", 3-1/4" blade lengths. These knives can also be opened using the flipper, and the grip pressure on the handle is transferred to the locking device in a way that is meant to increase locking pressure. They're available in the $80 to $120 range, depending on blade size.
I don't have any of these models but had some experience in the field with the 4" model owned by a friend, and was very impressed with the performance, quality, and design.