A sad story for both over the past five years; however, I'd still take PFE over MRK. The only way MRK outperforms PFE is by taking small time periods out of the overall trend. Not exactly a fair comparison.
I agree Pfizer is a btter company, however it is clear to me that since Merck dumped their CEO they have out performed Pfizer but a significant level. I think Mrk is up about 25% in the last 3 months and Pfe is up about 2%.