I've dived both of these BC's recently. They're both great.
The general concensus with most scuba divers, me included, is that the extra security of the buckles was more of a benefit (and more often used) than the one-step ditchability of the SeaQuest. Both were great and both had their advantages. Neither were really all that different... The velcro really was pretty secure, just not quite as secure as the buckles. The buckles took a sorta half-step more to release, but it really wasn't much of an issue.
Like someone else mentioned, though, there was a bigger difference in the cam straps... And that Scubapro design is really hard to beat. The SeaQuest design, by comparison, really isn't as durable or as secure.
The Scubapros also have this very interesting way of attaching themselves to your body, and allowing the bladder to "glide" back and forth on a set of hidden straps which reduced the amount of squeeze that it placed on your body. I liked it, and preferred it to the way the SeaQuest was: more like a hard-mount to your body.
So I personally liked the Scubapro better.
That said, keep in mind that the SeaQuest QD is their top of the line jacket style BC... There are color options and "gadget" options, but the design is the same throughout the QD lineup. And the Scubapro Glide is NOT Scubapro's top of the line jacket style BCD. So you really aren't comparing top of the line with top of the line. You're comparing SeaQuest's top of the line with Scubapro's mid-line jacket BC... And the mid-line Scubapro still seemed nicer to me.
The top of the line Scubapro jacket style BC is the "Classic," which is hand made in their factory, strapless in the chest, and has an all-over bladder that allows for the "bubble" in the bladder to go whereever it wants to, so as to not ever cause trim issues. It looks a little plain in the shop, but it dives great, and if it fits you well (more important, since this jacket forgoes the ability to adjust torso length like most do) you'll quickly become addicted to the BC's ability to have completely neutral trim in the water. At least, I was. The Classic also had the ability to accept either singles or double tanks, as did the SeaQuest QD... I don't remember if the Glide could be set up easily for doubles. That might be a decision maker for you.
FYI: Both the Scubapro's and SeaQuest's integrated octos are balanced this year, so that really shouldn't be a decision maker. I did like the look of the SeaQuest's integrated dump hose, designed to hold the low pressure inflator hose so as to appear to be one streamlined unit. However, in the water, I found it to be more of a pain than anything else, often snapping out of place unless you had "just the right length" of inflator hose to attach to it. This was never an issue with the simpler, although not as pretty Scubapro unit, and I preferred that to the SeaQuest for that reason.
Bottom line is that I don't think you could go wrong with either excellent unit, based on my humble experience... But my personal favorite was the Scubapro lineup, with a slant toward their top of the line "Classic."