This is really down to the kind of environment you want to be in, because Newcastle and Lancaster are totally different in almost every way. BTW I know this because I have family in Newcastle, so I visit there a lot, and I went to Lancaster Uni.
Newcastle is a city uni, the city is big and lively, loads of shops, pubs, clubs, concerts, theatres, cinemas on your doorstep 7 days a week. It's also quite "trendy", even a bit "Rah" in parts at the moment. Lancaster is a campus on a hill outside a comparatively small city. There is stuff to do, but the choice is restricted, and student life tends to revolve around on-campus events, bars and trips to the city or out to Morecambe, Preston or Blackpool. The atmosphere is totally different, and there is a bit of a "bubble" feel to it. It's friendly, cosy, comfortable.
When you visit Lancaster you will either think "I love this, it feels right" or "No way I could live here for 3 years." You should probably listen to that feeling. Course requirements and content are important, but what matters most is how happy you are in the place you have to live in for three long years.
I loved Lancaster, but I have to admit that it is not right for everyone.