I'd rather keep Eaves, because while Miller is better at this point he's not better enough to justify the cap hit above Eaves' current contract that he would end up with.
Emmerton, Andersson, Helm, Zetterberg, Datsyuk, Filppula (?) are all capable penalty killers.
There's no reason to keep either of these guys on when we can replace them with Nyquist, Tatar, Sheahan, Jarnkrok, etc. and perhaps a good free agent.
Here's the Wings' current roster for next year among signed players:
---/Zetterberg/Samuelsson
---/Datsyuk/Franzen
Abdelkader/Helm/Tatar
---/Emmerton/Tootoo
Eaves
Kronwall/Ericsson
Dekeyser/Quincey
Colaiacovo/Lashoff
Mrazek
Gustavsson
About $18m left in cap space.
As you can see, there's a bit of work to be done. Let's add in the RFAs (in bold) to get this:
---/Zetterberg/Samuelsson
Nyquist/Datsyuk/Franzen
Abdelkader/Helm/Tatar
Andersson/Emmerton/Tootoo
Eaves
Kronwall/Ericsson
Kindl/Dekeyser
Smith/Quincey
Colaiacovo/Lashoff
Mrazek
Gustavsson
This is all assuming Bertuzzi is on LTIR, of course. That's ~$2m that can be used elsewhere. Those RFAs just cost about $5m total, maybe even $6m. And the roster's full. But we have two amnesty buyouts and Colaiacovo is sitting as a spare, and Lashoff also. So we can buy out Cola or send Lashoff down. Holland would probably do the latter, gaining back almost $1m. So figure the Wings have ~$14.5m to spend on Howard, Filppula (or replacement), and perhaps another forward. In addition, trading Eaves opens up $1.2m AND a roster spot that can be used on one of Jarnkrok or Sheahan. There's no point to keeping Eaves as a PK specialist at that price if he's just the spare forward. Use that money for better players.