Robin, my unscientific observation is that you are more likely to have a not difficult baby than an easy one. Not difficult meaning either easy or neither difficult nor easy ie some aspects are easy eg sleep or eating, but others are difficult eg crying.
Also, 6 months is a tiny part of a child's life. An easy baby may become a difficult toddler. Sleep can fall apart at any time - so I would not count my chickens.
If you did end up with a difficult baby (strongwilled, won't be put down, light/non-sleeper, fussy eater - my dd was all of the above, as was ds, except for the eating), I don't think that is a bad thing. For one thing, babyhood, which is the most frustrating part for such a baby because they can't do anything for themselves, is a relatively short period. You will find that things get better and better. And when they start to move around and become toddlers, when other mothers start complaining about their easy babies becoming a handful, you just think how much more settled yours is.
I agree with mummytheresa that you bond better with a difficult baby - heck, you have no choice, because they DEMAND it. All the traits that make difficult babies demanding as babies (persistence, activeness, curiousity, cuddliness), makes them fabulous adults. I have never admired a laid back adult (although it is always touted as a good thing for a baby). The adults I have admired have always been go-getters who took initiative to make things better and improve themselves.
That is not to say a laid back baby will be a laid back adult. At 6 months, personality is not quite formed. Just wanted you to see the longer term view.
I am sure it will be fine in the grand scheme of things, whatever dc2 turns out to be!