Hello,
It sounds like you have an awesome trip lined up so far with tons of stops! Lisbon and Brussels/Bruges have a lot to offer, so it depends a bit on what you are looking for. Both will have decent nightlife if you know where to go.
Lisbon has a laid back atmosphere, a lovely seaside with palm trees, and some sweet monuments including the world's most expensive chapel. I think it is fair to call it a little "gritty" which may be a plus or minus for you. But taking in the view and a drink at one of the rooftop bars on a warm evening is awesome.
Brussels is a little more clean cut and has the Atomium which is definitely cool to see. There is also MiniEurope there by the Atomium which is kind of silly but also kind of awesome. Apparently there is a new Parliamentary visitor center (the Parlamentarium) which is the largest in Europe and really interesting sounding to me.
If your decision wasn't hard enough already, I'll add one more place to consider:
Zurich. I feel like it gets overlooked on a lot of people's Europe itineraries, but it's beautiful and has legendary nightlife. The old town is great and there are free public bike rental kiosks so you can ride all over town. Plus the Swiss Franc just took a nosedive so the exchange rate from dollars is looking pretty good right about now.
Good luck and have fun!
I would rather go to Belgium. In Portugal, the people can be very rude. Especially towards Americans.
If you're looking for nightlife then Bruges is not the place to go. It's called quaint for a reason. Brussels and Antwerp both have some fantastic nightlife, Leuven and Ghent are good too.
Lisbon if you want a nice holiday, Brussels if you want a city break