One of the tradeoffs I've had to make since switching from a DSLR (Canon 40D) to a compact mirrorless camera (NEX-C3) is using fewer manual controls and dials. This didn't bother me at first, given I was (and still am) pretty inexperienced with the many ways a camera can be configured on the fly for different shots, and the NEX's single programmable control dial in the back was sufficient for most of my needs--ie. changing aperture. But after using the RX1 for a little bit at CES, I remembered how much of a different manual controls really make, and that a compact camera doesn't have to sacrifice physical controls for size.
Whenever I get a new camera to test, the first thing I do with it is jump into the menus and see if any of its dials and buttons are configurable. Most entry-level compact mirrorless cameras come with just one dial in the back--which sometimes doubles as a four-way directional pad--accompanied by a few buttons. Not all of these buttons are configurable; they're often locked into functions like playback, video record, or fixed depending on the PASM mode.
For shooting in Aperture priority (my go-to right now), a lone dial will always be set to the F-stop as the default setting. Programmable buttons then change the function of that dial, which is when I start thinking about what's most comfortable for my thumb (or any finger other than my index, used for the shutter) to reach. I mentally rank the programmable buttons in order of accessibility. On a typical four-way directional dial, accessibility from best to worst goes like this: left, right, top, down. Some newer cameras will have a Fn button to let you cycle through settings, which I treat as a wild card.
So how to best program those customizable buttons? It's a personal preference depending on the settings you're most comfortable with, or at least the ones you know will have the biggest effect on the image depending on what environments you shoot most in. My button configuration is informed by my obsession with image quality. I used to think that that ISO was the most important setting to change on a camera, but since I'm almost addicted to the awesome image quality offered by an APS-C or larger sensor, I change ISO as a last resort. Bumping up the ISO higher than the 200 (the minimum for my camera) means I'm accepting grain in my images. For me, that's like turning texture quality down or reducing resolution in a PC game to get better framerates--I'd rather sacrifice something else for optimal image quality.
Instead, the setting I need to change most is exposure compensation. Adjusting down a third or two thirds of a stop means the camera has better tolerance for low-light images, and won't slow down the shutter speed as much to take an acceptable shot. In fact, my camera is almost always set to 1/3 stops down by default.
Next up is white balance, which I'm still figuring out. This is one area where presets really help--I can set the white balance based on the dominant light source (daylight, incandescent, fluorescent, etc) and calibrate based on that. After white balance comes ISO and drive mode (single, continuous, HDR, etc). Settings I rarely touch because I'm not comfortable changing then yet: light metering and exposure bracketing.
Of course, this is all under the assumption that I'm shooting in either Aperture or Shutter priority modes. In full manual, I would want independent dials for aperture and shutter, instead of one dial switching between the two with the press of a function button. That's why for my next camera, I want at least three configurable dials--two I'd set to aperture and shutter, and one I'd cycle between exposure comp, white balance, and ISO. I got a taste of that while shooting a few photos with the RX1, but I don't want to pay a huge premium for dials (though the clicky analog dial for exposure comp felt amazing). And it's unfortunate that some compact camera makers are moving even further away from physical controls with touchscreen interfaces--I see it as a real dumbing down of camera design.
How do you customize your own cameras, and what are the settings you need access to most when shooting?