Haven't played one, but generally a shorter scale will sound and feel more guitar like. I have a 26.5" baritone, and it is easy to play, and is still pretty good at communicating the depth of a lower tuning.
I’d go for the longer scale. If you’re planning to tune B to B, it will sound much clearer. If you’re hoping for A to A, then even 28” is shorter than I’d really want.
I would go long. I have an OLP 30" bari and I think that the relatively high string tension on the long scale contributes to its good tone. I have it tuned to open C with 13-56 strings. It sounds even better in open D with the same strings, but the string tension becomes scary. The way is see it, 26.5" is only one fret longer than a standard guitar scale, and 28"is about two frets, so they aren't adding much.
I play 7s with slightly longer scales in low B to E like the Rev and they sound awesome. If you wanna tune to A, maybe a longer scale would sound better. However, I am VERY impressed with Reverends (I have a Warhawk 390 that is wonderful) and think you oughta try out the Reverend in person. You might be as impressed as I am...
This is a good video that does a decent comparison.
Obviously, a shorter scale guitar wont sound like a Bass VI, but it is just different by design. For me, the short scale, a set of 12-62's, tuned to C, all makes for some cool tones.