Here are my three favorite spots for viewing the Eiffel Tower:
1) at dusk on the Esplanade of the Palais du Chaillot. Metro: Trocadero
2) for nighttime viewing, take one of the Seine riverboats rides (Pont d’Alma or Pont Neuf). We usually take the Vedettes du Pont Neuf, but any of the famous lines such as Bateaux Mouches our Bateaux Parisiens will take you past the Eiffel Tower. If you’d like a sneak preview, check out Les Vedettes de Pont Neuf video of the Eiffel Tower and fireworks.
3) for nighttime viewing, I’d recommend having a drink at the top of Tour Montparnasse. The cost of the drink is definitely worth the view!