Which is better?

Each type of marquee has their own benefits. Aluminium structures' main benefit is that there are no poles in the structure.

This allows you to place furniture dance floors etc. where ever you like, however, some people prefer the look of the traditional marquee and for weddings for example flowers can be trailed around the poles. Traditional marquees are generally quicker to erect and dismantle than aluminium structures allowing for a shorter stay on site. This is useful if for example you are renting a field and paying for this by the day.