Both programs are great and it really depends on what you want to actually do. If you're looking for a quick way to just drop and drag your folder into a program and search visually then SVG Viewer would be the program to choose. SVG Viewer will keep track historically on the folders you have searched. SVG Viewer only stores linked references to the SVG's. Meaning, if you move or delete the SVG file from your computer SVG Viewer is looking for that reference and will not be able to show the SVG.
If you're wanting a way to organize your files and search by tags/names then SVG Library would be the program of choice. SVG Library stores the RAW SVG data into the program's database. So if you delete or move the original SVG from your computer the SVG Library still has the RAW data and it will be able to export it on demand.