I've never felt bad about giving dps coms, and even prefer to do so. Tanks and healers are showered in coms for just being competent. DPS usually have to really stand out or the tank and healer both suck before they get considered. It does suck that we can only give one com at times. I've been in parties where everyone was just hitting every mark. I had to apologize to the others once since they all deserved marks imo. Those groups are fewer and far between unfortunately. Just give the com to whoever stands out for any reason. They'll get coms the next time or two around, I'm sure.