The question is which one is easiest to apply for and gives bigger credit lines?
From my reading on here, I would believe it would be DCU for bigger credit lines, and PenFed for eaiser to get into.
Penfed is, or at least was circa six months ago, incredibly conservative at least as far as their credit cards go; however, if you have a good credit report, they are a great CU.
DCU has much looser underwriting requirements: if you're a mixed file like I am, there's a lot more available, and while I'd mark them down slightly for some very confusing practices and awkward customer service stories I've heard, I've no complaints personally and they're still an excellent option once you're through the initial potential setup hassles who have been very good to me.
I have memberships at both, but I'm nowhere qualified for Penfed's credit card program; however, I may wind up talking to them for the stupid jumbo mortgage I may need. Penfed may be trying to change this a little bit, they're certainly on an email advertising blitz with me trying to get me to refi my auto loan with them among other products, but I haven't logged into the interface for a while to see if I actually have a pre-approval with them.
PenFed is much harder than DCU to get credit from. IE. PenFed has higher credit standards. However PenFed seems to be much more generous with CLs if you qualify. I think my initial card was like 25k or 30k. PenFed credit products are more attractive from a rewards standpoint and uniqueness even though they might no longer by world class products. DCU basically have vanilla 1% CCs. However DCU does give monthly free FICOs which is nice.
Don't forget about Alliant.