Im a total cross over cruiser. I'll sail anything that will let me onboard
across the gamut from budget to luxury.
I actually find it a big difficult to think about being devoted to one cruise line, even in the luxury line up.
I haven't sailed Crystal yet, but have been on Seabourn 3 times, Regent once (before they went all inclusive with tours etc) and most recently SilverSea.
I understand everyone had different parameters for what pleases them and makes them feel like they've had a totally luxurious experience, that totally meets their needs.
Of the lux lines, I will say that Silversea seemed like the best "fit" for me.