I actually haven't used anything besides the S1, and I find that it kills the center too much, so if the others you've tried are worse, then they must really suck. Recently I messed with the S1 in the mastering chain, and even just going from 1.00 to 1.25 made a noticeable difference in the center. I basically set it, closed my eyes, clicked the "bypass" button a few times so quickly that I couldn't tell if it was on or off, then used my ears to decide. Within about five seconds I could tell that the center was lost in one of them, and it was with the S1 turned on...
The custom made analog stereo widener that someone mentioned recently in another thread (used my Mika Jussila) sounds intriguing, although I don't really know of any analog wideners out there, and I would still be a bit scared of it. Analog of course does not definitely mean that the center will be preserved better, it probably works in about the same way.