Thanks a lot for advice. I have still more than a year ahead before I need to make a decision so there's enough time to ask around when I narrow my choices. I haven't even made my mind whether I want to get into neuroscience or stay in molecular/cell biology.

Sadly, the situation as you decribed is almost the same with PhD students in the lab where I currently work on my diploma thesis and in some around in the institute. Having seen what I've seen (troubles with disertations and giving the PhD defense go-ahead) that's definitely something I want to avoid.