What Lens do you most regret selling?

may be this thread could get into : which lens did you sold and bought back ?
because this is funnier

actually I sold my 17-35 AF-S, really regretted it but strangely in the meantime I didn't try to replace it, rather I tried not to use an UWA but that was useless. So after one year I bought an almost as new 17-35 of the last batch which is slightly lighter and seems shaper but that could be my brain playing... And now I'm happier than ever because it is way better than the original