Either is a great choice. If you use the Phera I think that going over 4 weeks and doing a 5th week would be a nice advantage, i think phera has a slightly longer halflife, kicks in later, for me strength gains were later, a 5th week would make a good cycle.
With Mdrol you're looking at faster gains but at 3 weeks how much LBM can you really put on? The 4th week makes it competitive, but some people aren't so compatible with Superdrol as to want a 4th week.
If you've done PHs previously and found them to provide good gains, go with Phera, it should be milder and a solid choice for adding quality weight. If your cycles felt really weak, you didn't get many side effects, go with Mdrol, it's straight up more powerful.