I can so relate to this thread!
Yes well DD1 had reflux and she was really hard work. Not just the reflux symptoms (hard enough in themselves) - which she grew out of - but she had to be held constantly, was super clingy (I couldn't even go to the toilet by myself) and so prone to overstimulation, like we couldn't have too many visitors or stay at someone's house for more than an hour or two because she'd be screaming all night and wouldn't sleep ... and she was incredibly frustrated in those early days, at not being able to move, and not being able to express herself.
Linzy - yes she improved HEAPS once she got more independent: once she got mobile, and once she could express herself through words. I think much of it was sheer frustration (well how would you feel if you wanted something and you couldn't walk over to grab it, or tell someone you wanted it?) ... so I like to think the brighter kids are harder work

(she has great speech for two and a half, anyway).
I could have stopped at one child, and felt a certain amount of apprehension - fear! - at going back for a second time, but like Hila, I am definitely more relaxed this time around. And there's not the huge learning curve of first-time parenthood to add to the challenges of having a difficult child.
However, I *think* (touch wood, very early days!) that DD2 is going to be more laid back than Clara was ... when she is not being bothered by her reflux pain, she is actually ok to be left for a few minutes - thank goodness, as I have a toddler now - Sheza I can't imagine how hard (impossible!) it would be having the difficult child second.
But yes their personalities definitely show through early on. I know toddlers are famous for wanting total independence, being demanding, strong willed, hugely entertaining and everything else, but DD1 has it in the extreme

(and she is also very sensitive, and shy) ... well I think she has it in the extreme, and other people comment on it - even strangers in shops etc, which I don't always appreciate, especially when they roll out the cliches like "oh you get one difficult one and one easy one" - which, as some of you can attest to, is not always the case.
There are definitely some 'character' genes in my family at least

... but DH was apparently a very placcid baby so maybe DD2 will take after him (once she outgrows the curse of reflux and we get the allergies/intolerances sorted).
But they may be demanding babies but they do make hugely entertaining (albeit still challenging!) toddlers - and I'm sure they'll grow up to be interesting people that others want to be around