According to PFF (which isn't perfect and I disagree with some how they do their grading)... but...
Packers have the 31st score in STs... with the Dolphins being 32nd.
Cardinals (68.9) and Ravens (67.9) are 16th and 17th... so I think 70 is supposed to be average grade, but average for this year right now would be 68.4.
Packers are close to beit dead last in grade still... Bears are #5, Vikings #9 and Lions are #21.
Trying to break down their grades more...
~ Kickoff return, Amari has 56.8
~ FGs grade, Crosby 66.5
~ Punting grade, O'Donnell 61.9
~ Kickoff, Crosby, 61.4
Then basically everyone whom has played on STs, I'm not listing them all...
But listing the top 5 in terms on snap count all with at least 28 ST snaps...
TE Davis 50.9
ILB McDuffie 73.7
OLB Galeai 53.4
S Leavitt 45.1
CB Nixon 48.1
To show some better ST grades, I'll also lis those with at least 18 ST snaps but less than 28...
CB Stokes 67.3
TE Dugara 73.6
WR Rodgers 60.5
CB Douglas 71.2
But the grades then go way down from there... I'll just mention the three worse ones...
ILB Barnes 29.6
CB Jeans-Charles 41.8
ILB Campbell 44.3