I guess I'll be the odd man out. I've used both styles on J-frames and I find the release to be more positive when doing speed reloads when using the new style latch, though I have to admit both work fine for me. I have a 642 no-dash with the old-style latch and a 642-1 with the new-style latch, and I'm considering getting a new style latch for the no-dash.
As far as shooting comfort, I've gotten "wear spots" on my thumb using either latch style, so no real difference to me in that regard, though I do like that the newer latch has more rounded edges than the older latch.