It's hard to say. I would have said Firebird at one point, but I started carrying a Predator because it's pink (the FB is yellow), and they're pretty well the same disc. I would have said Drone, but I discovered the Pain. So what would I say RIGHT NOW would never leave my bag?
1. Buzzz. Any Buzzz. Doesn't matter. I'm partial to FLX, but I've been throwing a Z recently. Have a 10 Year and a Cryztal asking for some air time too.
2. Gazelle. Any Gazelle. I always have at least one in the Lite bag, and at least four in the Comp bag. DX, Glo, KC Pro, or Star. They all fly similarly, but differently enough that I can use multiples in a round.
3. GL Pain. I've beaten mine in enough that it's semi-flippy, but it still goes exactly where I tell it to. My go-to mid for just about any shot.
4. Trident. I throw a GL, but it's getting flippier and (dare I say it) glidier with age. I should try an Opto and see what the difference is...
That's it. Everything else is expendable.