Best way to choose between DC Jack and USB power input

I would like to power a device from either a DC Jack, JST socket or a USB Socket and I'm curious, what's the best way to do this?

I examined the Arduino Uno R3 Schematic and the way they do it is somewhat involved (with more components than I would like at an SMD level). Is anyone aware of a TH IC that would just take multiple power inputs and handle the job for me?

It depends on what kind of "device" you are powering, and how much voltage/current you need, etc.

If you need 5V at low current, you can power it directly off USB, and if you want to optionally use a higher-voltage DC power adapter, you can use a voltage regulator. It usually doesn't hurt to leave the voltage regulator connected if you bypass it with 5V. But, you can also use one of those 0.1" jumper-plugs to connect to the desired input, or to bypass the regulator.

The simplest voltage regulators (for low current applications) are linear 3-terminal regulators (input, output, and ground). Usually the need a capacitor on the input and another on the output. Otherwise, they are very straight-forward to wire-up and use.

I think you misunderstand -- I'm not asking how I should power the device. What I'm asking is if the end-user plugs in the device with USB AND with a DC Jack, what circuitry could I use to take power from just one of those sources (and thus not frying the device by supplying current from multiple sources).

The idea of just using a switch the user can toggle is reasonable but I would prefer to have an automatic way.

i have had mine uno powered from an external 12v source and have had the 5v from the usb. from my understanding is it has built in logic that selects the power source.

built in logic that selects the power source.

That's true but I think SilentDirge wants a simpler approach.

Unfortunately I can't think of a single-chip solution although the MAX1551-MAX1555 would be close. These are LiPo chargers that select between the DC and USB inputs. Maybe there is a version that just switches without the charging or maybe you could coerce these chips into working.