When I did my degree, I ended up specialising in Physical Chemistry just because physical lab was the one I was least bad at. Though I did maths & further maths A-levels, I never have been particularly gifted in calculus - I never quite "got" things like integration and partial differential equations even at the time. Let alone now when I haven't used maths of that level in years. So I was never going to be very good at a lot of the quantum and thermodynamic stuff that requires that kind of pure maths. Then I ended up going into Environmental Chemistry, which is something I am good at - but it's not a good area for me to study from an emotional point of view. The problem with environmental research is that you can prove that something is extremely damaging and needs to be banned, and then it can take 5 years after your original paper before any other scientists listen to you, 10 years before pressure groups pick up on it, and a further 10 years before any legislation even starts going through governments. I like the idea that my research could change the world, but I find that waiting around for governments to act very stressful & upsetting. I'd much rather work in another field where I don't feel personally responsible for global warming.
Organic Chemistry was always my favourite at school, but I struggled with it horrendously at university - principally because we had one lecture teaching us skeletal formulae ("line notation"), and then every other organic lecture used skeletal formulae more or less exclusively. (I have, in fact, found most of my first year organic notes, and I'm not exaggerating!). I'd be sitting there trying to copy a diagram from the board with a certain number of wiggles: /\/\/ and having no idea at all how that related to a molecule. And if I got the number of wiggles wrong, I'd have drawn a completely different molecule and not even realise. Argh. Then the fact I had bloody awful organic tutoring and spent a lot of my degree clinically depressed without any useful medication made it impossible to catch up.
I don't know for certain that organic is what I want to do - I also want to study lots of Inorganic Chemistry. I've always liked Transition Metals, and the Lanthanide and Actinide course I took was amazing. I also enjoyed Acids & Bases and Non-Aqueous Solvents. I'm just sure it's all of that stuff I'm interested in and not Molecular Reaction Dynamics, Liquid Interfaces, Molecular Theory of Gases, Liquids and Solids or Chemistry of the Gas/Solid Interface.