I'd say it depends on the amount of lift you are after. An inch or bit more, a plate would do. Any more, and springs would be the better bet. Plus other suspension components are involved with larger lift heights.
Best to research sites that sell lift kits, plus the more experienced folks here that have had their BS's lifted. Here is when "don't go cheap" is good advice.
I have no experience in lifting a BS, but did run across this thread on this site this morning: