Both types have their issues. A
transformer wall wart runs hot. Some equipment relies on the
wall wart for adequate DC smoothing. That DC filtering is done by an electrolytic
capacitor whose life span is severely limited by heat. A better approach for equipment design is to use an AC output
wall wart, which puts all of the rectification and filtering, the parts that fail, where they belong, inside the equipment. Or, at least put enough filtering in the equipment that it'll still work OK when the
capacitor in the
wall wart dies. I have replaced piles of bad
transformer type wall warts.
As for switching supplies, a well designed one runs cool which means it might last longer. I like it when the
power supply is cool to the touch. They can sometimes radiate some RF, typically up into the low
VHF range. For wireless systems operating in the
UHF range, probably not a problem. Boston
Acoustics famously made an HD Radio whose own "
line lump"
power supply interfered badly with reception. It certainly doesn't hurt to keep switching supplies away from antennas. I suspect that switchers are cheaper now, which the manufacturers love.
Often times, the choice of which type to use is determined by the
power needs of the load. Transformers are seldom used for high
current loads (over a few hundred milliamps) because they get bigger, heavier, and more expensive very quickly as the
current goes up. Most digital wonder boxes need lots of
current.
Radio Shack makes some pretty good, regulated, switchable
voltage, and high
current wall warts. They are handy to have as a quick emergency replacement. I don't bother with their
adapter plugs. I just cut the
cord off the failed wart and splice old
cord to the new supply. That way I know the
plug really fits, the
polarity is correct and cannot be changed.