your L will be worthless if used with cheappo filter...
B+W & Hoya will mostly be recommended... all my L's have B+W except for 100L coz i have spare Sunpak multi coated UV.
You make your 100L sound "worthless".
TS, since your lens is pretty good glass, get a UV filter that can match it's glass quality. (i.e. don't be cheap)