best laptop for a university student? i travel abroad a lot, so it has to be useful in the EU and the USA?

Get a macbook air just so you can show off

Get a light weight laptop with 14.1 or 13.3 display and get a power inverter that will hook up with 220V AC for your power supply. Sony Vaio and Dell have several models for you to select from.

get the latest configurations + the most important part that it should have a 12 cell battery (or 2 batteries).

a 6 cell battery gives 2:30 hrs of backup (average) while it can give arnd 4 hrs backup with a 12 cell battery.
that is what matters when you are using it for educational purposes.

Get a Toshiba. They're tough and reliable and ask about their worldwide warranty, which you may need if it breaks down abroad.
Also make sure you have a copy of the purchase receipt in case the border customs want to make you pay import duty on it.

get a free laptop on this site instead of buying retail