Live view autofocus on Pentax cameras

You ask "which of the recent Pentax cameras offers the best AF via the LCD". I can't answer which one offers the best. I do use AF via the LCD when shooting landscapes on my KP, and it works perfectly well. The AF area is a square of fixed size that can be positioned almost anywhere in the frame, or locked to the centre. It is white, and turns green when achieving focus, or red if focus cannot be obtained.

Other AF Active Area options for Live View, which I do not use, are Face Detection, Tracking, and Multiple AF Points. For the latter, the sensor is divided into 35 areas (7 horizontal by 5 vertical), from which you can select and position a rectangular array of 1, 9, 15, 25, or 35 of those AF areas.

AF Active Area can be assigned to one of the customizable buttons on the camera, for quick and easy switching on the fly without entering the menu. Although it's available, I don't use it in LV, but I do sometimes use it for switching between Select and Spot in AF through the viewfinder. I don't even have to take my eye away from the viewfinder to do this.

In Live View, when AF Active Area is Select or Multiple AF Points, and you are positioning the AF area, pressing the Green button (a hard button next to the LCD) instantly returns the AF area to the centre of the frame.

Two types of focus peaking are available: Highlight Edge and Extract Edge. Both are a boon to manual focusing in Live View, especially when combined with magnification, which is available up to 16x. In magnified view, after you have panned around the image, the Green button returns the magnified area to the centre of the frame.

Histogram Display and Highlight Alert (the blinkies) are both available options for Live View.

The KP has a tilting screen, not a "selfie screen". I find tilting it very useful, and have never had a problem with it in nearly five years of use. An Arca-Swiss plate is permanently attached to my camera, without interfering with the screen.

One or more of the features mentioned above (besides the tilting screen) are not available on the K-3.

I use manual-focus Zeiss and Voigtländer lenses on my KP. Of course, they are a pleasure to focus using focus peaking in magnified Live View on a tilted screen. The ergonomics - and the results - are excellent.

The one drawback I would point out is poorer battery life when using Live View on the KP, compared to the K-5 and K-3 lines of cameras.

The KP is discontinued, unfortunately, but available on the used market.