I think you will find the sociability factor on Crystal to be superior to Silversea, mostly because they have bigger ships and more passengers. They always have gentlemen hosts onboard to dance with the ladies.
They also have an abindance of activities during the day with tons of lectures, movies, classes etc. It os one of the most active cruises I have ever been on. This also makes socializing much easier.
The advantage Silversae has is that they are far more destination focused - you are likely to spend far more time in port on a Silversea cruise than on Crystal - but that also depends on the cruising region. Crystal tends to offer more ports of call in Europe than they do in The Caribbean, for example.
Silversea has wonderful food and excellent service, but there is no gurarantee that you will be able to socialize as much as you would like to because the ships are smaller and will be occupied mostly by couples. They also attract for non-U.S. cruisers so there could be a language barrier to you making friends.