Eiffel tower tickets not available is the montparnasse towers
worth it as an alternative? If yes do we need to obtain tickets in advance
It isn't about the view IMHO so going to the top of this ugly modern building is noway the equivalent. for good views high up you can go for free to the top of the Institute Monde Arabe or top of Gallaries Lafayette. I'd go to the top of the Arc du Triomphe rather than the Montparnasse Tower. You don't need to book the MT ahead -- and if it IS the view you are anxious to have, it is a good one.
But when is your trip? Most tickets for the ET are released exactly 7 days ahead at 1 pm Paris time. If you still have time I would do a dry run so you know exactly what the site requires and can be set up and ready to go at 1 PM Paris time. there will be a rush and so you have to persist till you get through BUT that is when most tickets to the summit are released and you probably get them if you attempt it then.
Or if you are fit and want the experience, the line to buy tickets to walk to the second floor with an add on elevator ticket from 2 to 3 is usually pretty short. The wait is not the hour or two you would have otherwise.
They say the best view in Paris is from the Montparnasse Tower. Why? Because its the only view of Paris that does not include the ugly Montparnasse Tower.
That said, my favourite view of Paris is from the Arc de Triomphe. Eiffel Tower view is not great because it is SO high, you can't see much detail below.
Another vote for Galeries Lafayette. Not only do you get a great view from the top, but the inside of the building is gorgeous. It's also just fun to stroll through and pretend you are rich and could actually afford to buy something.