^^^^ Pay attention to SaintGimp's comment re: noise and ripple on SMPSs. For a bench supply, I would scratch them off the list right away.
3A is a LOT. Sure, there might be audio projects that take more, but I would suspect a dedicated supply would be used.
Most microcontroller and transistor projects are going to take far less than 1A, probably around 100 mA.
So, of the two, I would probably think about the 3A but if I could still get the 5A for $30 more, I guess I would do it. If I had to pay $400 for the 5A Mastech, I would buy the Rigol DP832 - which I have.
It's too bad the 5V is fixed. There is a tendency to run microcontroller projects at 3.3V. Yes, another regulator on the prototype board will work but it's not as cool as an adjustable 5V supply.