I have now tried the BOSS VE-20, VE-2, VE-5, and VE-8. What I want is great vocal processing, and harmonizing. I'm frustrated with features.
I have found that I cannot rely on guitar input to determine the tonal base (key) of the harmony. It's something to do with the way I play, which is finger-style and often somewhat staccato and percussive. I have to set the key before each song.
Also, I use a collection of different harmonies. I use some sort of harmony on about half of my songs now. Most of them are a high third, a high fifth, and (when I can get it) both combined. I have used other stranger harmonies on a handful of songs.
The main thing I'm looking for is the ability to set the harmony and the key without bending down to tweak a knob on the floor, when I'm on stage performing.
Here's a basic off-the-top-of-my-head assessment of each of the BOSS processors with my needs in mind. This is not an exhaustive analysis.
This unit has a lot of banks of customizable effects, and I could change them using my foot. But I'm pretty sure I would have to pre-set my favorite effects for each key I'm interested in. That is, a pre-set memory includes the key setting. This sucks.
I like this, and it got me used to those two-part harmonies. But there's only minimal control using an external foot switch -- three memories -- with the same problem as the VE-20. I'd still have to set the key. This is also the only unit of the ones I tried that does NOT have some kind of looping. Don't really use it yet, so it didn't bother me.
So far, my favorite unit. Mounts on a mic stand for easy access to setting without bending down, and I can punch the harmony in and out with an external foot switch. It's nice to have a little less on the floor -- lest clutter, and less chance of hitting the wrong pedal. Problem is, this unit doesn't have two-part harmonies! Why the F did they get rid of two-part harmonies?!?! Isn't there some way to download a firmware patch or something?! I've compensated because this unit has the ability to do 4th and 6th harmonies. But no two-part. Very disappointing.
Very fancy shmancy unit that includes guitar processing. Problem is, though I get my two-part harmonies back again (similar form-factor as the VE-2 in this regard), and I could set it up to change the harmony type and the key with external foot switches, I have now lost some control in the settings. It's a pretty complicated unit to use on stage -- would take a lot of getting used to. Also, no 6th or 4th harmonies.
All in all, I would sure love to see BOSS come out with a firmware patch for the VE-5 that includes some two-part harmony options. Like, a combination of +3 and +5. Or perhaps also the other options available on the VE-2 (high/low octaves, thirds, and fifths).