Crystal and Silversea are different products in many ways. Crystal has tried to become effectively as inclusive (or more inclusive) than Silversea by giving generous onboard credits. That way if you don't drink you can use your credits for the spa or shops or tours. If having seamless cruise where you don't need to sign for drinks is important to you, then Silversea better fits the bill.
There really isn't a cruise line that can touch Crystal's enrichment programs.
However, Silversea has open seating while Crystal has early, late and by reservation seating. That may be too restrictive for the same free flowing concept that goes with not signing for drinks. (Silversea's charging for some alternative dining does run contrary to its trend, while Crystal does not charge for same.)
For me, however, the fact that Silversea has suites and Crystal, save the upper categories, has small cabins is a big advantage for SS.
Another is the number of guests. Crystal has more than double the guests...but it does have many unique and enjoyable venues. It does not feel crowded, but also not as intimate.