Hi, I got offers to both schools as well, but for a different course. I'm currently doing my foundation year in Nottingham and I can say that the city is really good for students. I don't know anything about the sciences but I can talk about the student life.
The bus fares a really cheap at £1 each way and you can buy a day pass or an entire year's pass. Accommodation is also relatively cheap and you'll always find somewhere you like.
There are free hopper buses which run between campuses so it's quite convenient although it gets busy towards the end of the day
Generally, it safe, but I've heard of some parts which may not be safe, but you're less likely to find yourself there
If you're a party person then you'll enjoy the Nottingham night life, there are always parties and you even get flyers at your doorstep
The problem I have with York is that it's quite expensive to live in, and being located in the North, it will be really cold
What I can say is that you can't really find the perfect university, you just have to set your priorities straight, either the course programme or the student life, and all other things can be adjusted and will eventually fall into place.