Yes, a 1998 Nissan Maxima QX grill from a United States manufacturer will fit on a Nissan Maxima from Belgium if the two vehicles are the same year and make. The standards in the two vehicles are the same.
The maxima is a 3.0L while the altima is only a 2.4L. While the maxima only has 5-10 more horsepower, its extra cubic inches goes more twords torque. I would say maxima hands down. I personally have a 92 maxima, and it is not at all slow.