The cold steeping would lend less possible astringency from the coffee grounds and a cleaner flavor.
If you're adding it at bottling time from a cold steep, I wouldn't worry about boiling. There should be enough alcohol in your beer that it wouldn't stand a good chance of getting infected anyway. I've done the cold steep several times and I just pour it right into the bottling bucket or keg. Works fine.
Believe it or not, a guy from Maryland won our tri-club winter ale competition with his coffee stout. When asked after winning how he added the coffee to the beer, all he said was, "Right before I bottled, I just brewed up a batch of coffee on the machine and poured that sh*t in there once it cooled down." Seemed to work well enough for him, and I can't disagree with his technique - it was a great beer!