Tie between Benchmade and Spyderco. Both make some great knives.
I dislike liner locks and frame locks. That rules out a lot of the more expensive brands.
I like serrations. Benchmade has excellent combo blades but no fully serrated blades that I am aware of. Spyderco's combo blades have funky grinds, but they have some good fully serrated blades.
I like knives that can be opened with a thumb or finger flick, which includes almost all manual Benchmade knives and most non-thread-locked Spydercos with compression locks. I am willing to settle for a wrist flick on some Spydercos that are fully serrated or have special steel such as LC200N.
Benchmade has much better quality control, but their choices in steel and handle colors are a little boring. Spyderco knives with compression locks are excellent when they are not thread locked, but their lockbacks are hit or miss.
Particular Benchmade knives: Rukus II, Mediator, Volli, Bugout, Griptilian, Nakamura, Mini Adamas
Particular Spyderco knives: Para 3, PM 2, Pacific Salt 2, Salt 2, Caribbean Salt, Sliverax, Yojimbo 2, Canis
Other brands: Protech Malibu, Civivi Cogent, We Ziffius and Exciton, Cold Steel Ultimate Hunter, Kunwu Pulsar, Kizer Cormorant
Fixed blades: Gerber Strongarm, Mora Kansbol, Cold Steel AK-47, Ruike Hornet F815, ESEE Xancudo 3 S35VN, ESEE 4 S35VN