Flyers fan here..
Still a pretty weak group, but they will be better than last year just by not having Berube around..and they will soon be replaced by some really great prospects. Here is how I see the pairs breaking down.
Schultz-Del Zotto
Both played well last year. Schultz was a pleasant surprise and rarely made a bad play. Really poised, simple defensemen. Del Zotto was electrifying at points. 32 points in 64 games. Showed a lot of perserverance and found his game again. Will get caught out of position on the rush but actually defends the cycle pretty well for a lighter guy.
Medvedev-Streit
I don't know much about Medvedev other than he is supposedly a good two-way defensemen that can move the puck efficiently. Streit has been good the past two seasons but defensively, he is just a smarter version of Del Zotto. He will get caught out of position and has slower recovery speed than the elite defensemen of the league. If Medvedev pans out, they are a good 2nd pairing, but not great.
MacDonald-Gudas
MacDonald has been a disaster here. He's now paid like a top defensemen but won't sniff top 4 minutes. If we could move him, we would, but we can't. Should be ok in a bottom pair role. This pair won't see any minutes in significant situations.
I expect Luke Schenn and Nik Grossmann to be moved this summer. Both only have 1 year left on their contracts and are redundant with the addition of Gudas.
Shayne Gostisbehere and Samuel Morin will both likely start the year in the AHL but should see NHL time and 1, if not both, will be regulars by the end of the season.
I can see the Flyers moving Schultz and/or Streit at the deadline to contenders for picks, freeing up spots for the aforementioned prospects.