Boy, as far as accuracy is concerned, I really can't say if there is much of a difference. For the most part, "Benchtop" seems to always be more expensive than portable.
I like a meter that handles more complex AC waveforms than just sine waves, but I really can't say what specs describe that ability. The ability to accurately measure AC riding on top of DC is good, too, but again, I don't know what spec describes this.
You might see something that has additional features you might find useful. Recently, I would have liked a meter to check a high Voltage diode out of a microwave oven; turns out most meters don't supply enough Voltage to turn one of those on. I have a meter with the capability to test frequency in the audio bandwidth which is useful, and it also has a limited range of capacitance reading; it won't check capacitance at anything near operating Voltage, though, so it is pretty limited.
If I was to go for something strictly for use on the bench, though, I think I might opt for one with a large LED display so that it is easy to read from a distance and at an angle. LCDs are great for saving batteries, but if saving batteries is not the issue, then big and bright is preferable, IMO.
