Concern about opening folders quickly and consistently can be addressed the old fashioned way: lotsa practice. Standing around flicking your knife open can get kinda boring; instead I suggest incorporating use of your knife into every daily task you can. Open your mail with it, cut your steak, prune the shrubs, stir your coffee, open boxes, and so on. It won't happen overnight, but eventually you'll find your knife leaps into your hand before you knew you needed it.
As for fixed blade suggestions, sheesh, where to start? A couple notions you are unlikely to hear anywhere else: First, at least initially, don't buy anything you can't toss down a storm drain without losing sleep. Concealed fixed blades are going to be frowned on in most jurisdictions; buy something you won't think twice about tossing in the bushes if you have to. Second, make sure whatever you buy can be drawn and resheathed quietly. If you have reason to draw a knife in combat then you also have reason to do so without telegraphing your intentions.
Beyond that my advice would be to figure out what blade style you favor and then pick up something relatively cheap in that style. Cold Steel has a lot of options in the $50 range. CRKT, Becker, Kershaw, Gerber, also have knives worth looking at. Once you've settled on a blade style that works for you, and if your pockets are plenty deep, there are a lot of folks other there making many amazing knives. Some of my favorites are Strider, Simonovich, Hossom, Terzoula, among others. There is no shortage of options, in other words. The hard part is narrowing things down.
