Is baguazhang better than tai chi chuan?

No.
It is a different tool designed to do a different job.
Baguazhang is intended with multiple opponents in mind.

Tai chi chuan is the better art to learn overall because virtually anyone can study tai chi.
The skills are sophisticated and subtle, but accessible for the patient student.
As a combat system it is pragmatic, versatile and functional.
There is very little risk of injury.
The art is gentle on the body.

Baguazhang is not so easy to learn, arduous on the body, harder to understand and not straightforward to apply.
It is not so good for people who have health problems.

So why bother?
Because it is effective, fun and challenging.